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Glossary of Unreal Engine Terms

Document Summary: This is a complete glossary of all the Unreal Engine terms you will ever need to know.

Document Changelog: Maintained by Richard Nalezynski?.

A - B - C - D- E - F - G - H - I, J & K - L - M - N & O - P - Q & R - R - S - T - U - V - W - X, Y & Z


Actor - An object that can be placed or spawned in the world. This includes such things as the Players, Weapons, StaticMeshes, Emitters, Infos, Sounds, etc.

ActorX - An exporting plugin used for exporting skeletal meshes and their animations into files that Unreal Ed can import. For more about the ActorX plugin, including downloads, see the ActorX document.

Additive BSP - BSP space that has been added to a subtracted BSP space. Additive BSP is solid, impenetrable space within the game environment. See BSP.

AI - (Artificial Intelligence) A term used to describe the behavior and apparent thought process of computer controlled characters. This can include things as simple as non interactive scripted sequences to things as complex as computer characters that learn from player actions and adapt.

AI Controller - A class that defines how a computer controlled characters or a group of computer controlled characters behave.

Alpha Channel - An extra channel in a texture that allows for not only transparency but also translucency in a texture. To use an Alpha Channel one must have the texture's bAlphaTexture property set to True. For more on Alpha Channels, see the Texturing and Materials document.

AmbientSound - An actor that when placed in the level will loop a sound file selected from the Sound Browser. For more on AmbientSounds, see the Audio System document.

Anim/Animation - Movement created for a 3D model with bones that allows it to move in game. The Animations are stored in .PSA files and several can be imported for a single skeletal mesh.

AnimNode - A single component of an AnimTree. Many different types of AnimNode are connected together to form complicated procedural animation blends.

AnimTree - An animation setup applied to a skeletal mesh, containing multiple animations, blends and skeletal bone controllers.

AnimTreeEditor - The tool within the Unreal Editor which is used to create and preview AnimTrees.


Beam Emitter - An individual emitter that stretches a texture into long strips and emits these strips in a pattern that can be designed in within the Unreal Editor. For more on information on Beam Emitters, see the Beam Emitter Reference.

Blocking Volume - A volume that can be created in the Editor that will block players as well as other actors, but it will not block zero extent trances. For more on Blocking Volumes, see the Collision Reference document.

Bot - A computer controlled player that has its own AI.

Browser - One of the tabbed menus that one can use to view various aspects of the editor. For more on these Browsers, see the UnrealEd User Guide document.

Brush - Any geometry created from the Brush Primitive tools on the left side of the Unreal Editor including the red Builder Brush. For more on Brushes see the BSP Brushes Tutorial document.

Build - The act of compiling the level so that it can perform all of the necessary precalculations such as lighting, path generation, and resolving geometry. Also known as Rebuilding,
          - The version of the Unreal Editor. For example: UT2003 uses the 2136 Build of the Engine and UT2004 uses the 3186 Build of the Engine. Unreal Engin3 3 is distributed in QA-Approved Builds (Release Notes). For more information on the various versions of the Unreal Engine, see the Unreal Technology Roadmap document.

Builder Brush - The red Brush that one can use to subtract out or add in BSP volumes to the level. For more on the Builder Brush, see the UsingBSP Brushes document.

BSP - Binary Space Partitioning (sometimes refered to as CSG ) is a data structure that is used to organize objects within a space of the level. While it is not semantically correct to use this term to refer to geometry, it is loosely accepted as referring to the geometry created with the builder brush. For more on BSP, see the Using BSP Brushes document.
      In simpler words, BSP is a type of geometry that can be added or subtracted from a level to sculpt the space of the environment.

BSP Holes - Inexplicable breaks in the BSP geometry where subtractive and additive BSP spaces spill into each other. They can occur in highly complicated BSP additions/subtractions. In addition to slowing down the frame rate of a scene, they have been known cause other more strange problems including but not limited to disappearing staticmeshes and invisible player blocking walls.


Camera - The view that the player sees from in game as well as in the Unreal Editor. In the orthogonal viewports, one can see the Camera for the perspective view shown as an eye.

CollisionCylinder - The cylindrical space around every actor that can be used to determine collisions. For many actors, this setting is by default turned off but for other actors such as the player and triggers, the CollisionCylinder is on be default and detects when other actors collide with it. The height and radius of the CollisionCylinder can be altered under the collision properties tab.

Collision Model - Less complicated geometric volumes that are created along with and stored in a staticmesh. The Collision Model is used to facilitate faster collision calculations than would be possible with just a complex staticmesh. For more on Collision Modles, see the Collision Reference document.

Commandlet - Commandlets are an optional parameter you can give Your Game executable to perform various actions or output information. See the Commandlet List and Making a Commandlet documents.

Console - (a.k.a. command prompt, command line) A field at the bottom of the Unreal Editor that allows one to enter console commands in the editor. For more on the Console, see the Console Commands document.

CSG - Constructive Solid Geometry (a.k.a. CSG ) this is a more semantically accurate term for BSP (Binary Space Partitioning). The term CSG refers to the geometry created with the builder brush. For more on CSG, see the Using BSP Brushes document.

Cubemap - A Cubemap is required to create an environment map which can be used to create the appearance of a reflective material. To learn more about Cubemaps, see the Materials Compendium document.

Cull - To hide from the rendered, or in other words, to have the rendered not draw something.


Decolayer - A layer in the terrain that can be used to generate a set random pattern of staticmeshes that will remain attached to the terrain and have their scale and orientation randomly skewed per instance of the staticmesh. For more on Decolayers see the Terrain Editor User Guide document.

Deintersect - An action that will leave the remainder of builder brush selection that is in negative/subtracted space. For more on using the Deintersect button, see the UnrealEd User Guide document.

Demiurge - A Platonic deity who orders or fashions the material world out of chaos. See also Demiurge Studios.

Drag Grid - (a.k.a. Grid) A toggle that allows one to snap certain actors (such as staticmeshes, movers, and brushes) to a grid in the Unreal Editor. The Drag Grid size can be adjusted by powers of 2 going from as low as 1 to as high as 4096. To learn more about the Drag Grid, see the UnrealEd User Guide document.

DXTC - (a.k.a. DirectX Texture Compression ) A method of texture compression that is the primary algorithm for texture compression in the Unreal Editor.


Emitter - (a.k.a. Particle System) An actor that can spawn a series of other actors such as staticmeshes and sprites as particles to achieve various special effects. Emitters can be used in conjunction with each other to create "Particle Systems." To learn more about Emitters, see the Particle System Reference document.

EnvMap - (a.k.a. EnvironmentMap) A type of material which can be used to create the appearance of a reflective material. To learn more about EnvMaps, see the Materials Compendium document.

Event - A call that certain actors can listen for that will cause them to initiate some action. Events can be called from triggers, movers, emitters, and from code.


Face - One side of a BSP object. A Face is made up of two triangles.

FaceFX - A tool integrated into the Unreal Engine that allows one to animate lip synching to character models. To learn more about the plugin, see the Introduction to FaceFX document.

FPS - (Frames Per Second) A measure of the rate at which pictures are shown for a motion video. Television runs at roughly 30 FPS, film usually runs at 24 FPS, while games often have variation in their FPS.
          - (First Person Shooter) A style of game that depicts the scene from a first person perspective and the primary interaction with the world is a gun of some sort.


Garbage collection - Automatic destruction of unreferenced objects (as in Java, C# or UnrealScript)

G16 - Grayscale 16B image. Terrain uses G16 bitmaps for the heightmaps and alpha layers.

Geometry - Anything constructed out of triangles in the level, such as StaticMeshes, BSP, Terrain, etc.

Grid - See Drag Grid.

Group - (Groups Browser) Actors can be assigned to a Group using the Groups Browser. These Groups can be used to better visually manage all the different actors that can clutter up a scene. To learn more about using these Groups see the Groups Browser Reference? document.
          - (Package Groups ) A subdivision of assets within a package (such as a texture, staticmesh, and sound packages) that allows for easier management of the assets within the browser.


HOM - (Hall of Mirrors) An effect where the renderer does not correctly redraw the scene creating a chaotic visual effect similar in appearance to a Hall of Mirrors. This effect can be caused by looking into an antiportal or through a BSP hole in the level.

I , J & K

Impersonator - A tool integrated into the Unreal Engine that allows one to animate lip synching to character models. See FaceFX.

Instance - a) object of any class; b) subobject created based on a template, contained within an object instance

Intersect - An action that will leave only the section of the builder brush that is overlapping with additive BSP geometry. For more on using the Intersect button, see the Editor Buttons document.

Invisible - A surface property for BSP geometry that will cause surfaces marked as Invisible not to be rendered. Invisible surfaces however will still collide as if they were visible.

KActor - A moveable staticmesh that uses the physics engine to collide with other world geometry with realistic physics. KActors are a single rigid body.

KAsset - An instance of a PhysicsAsset in a level. KAssets use physics to drive a skeletal mesh, so are good for placed ragdolls, or other skinned objects made up of multiple rigid bodies and joints.

Karma - The physics engine by Math Engine which was integrated into Unreal Engine 2. Unreal Engine 3 uses the Ageia (formerly Novodex) PhysX engine.

Keyframe - A pose in an animation or mover path that is used to interpolate the motion of an animation or of the movement of a mover.


Layers System - (Layers) A mechanism to allow multiple people to work on the same map simultaneously. A layer is a slice of a map which can be edited individually of other slices. An example of this workflow would be one layer for lighting and one layer for geometry, allowing two people to work on those areas of the map independently and without overlap.

Level - A level defines a set of actors and other complex data that can be loaded and unloaded atomically. The world in Unreal Engine 3 may consist of many levels; a typical game may contain several hundred individual levels. These levels may be dynamically loaded and unloaded based on proximity, explicit load/unload triggers, and other criteria. For more info on levels, see the Creating Levels and Level Streaming documents.

Light - An actor that casts light on the nearby surfaces.

Light-map - A technique used by Unreal Engine 3 to encode the light hitting a surface, including an approximation of the direction the light is coming from.

Lightwave - A 3rd party modeling program that can be used for creating intricate staticmeshes and/or skeletal meshes.

LOD - (Level of Detail) A feature that allows the resolution of the geometry to decrease over distance in order to increase the frame rate of a scene (specifically in animated characters). For more on how to use LOD on models, see the Static Mesh Editor User Guide document.

Log - A window that prints out actions either in game or in the editor that shows every action that takes place.


Map - The file that is saved which contains all of the placed actor properties and thus the layout of the entire scene you've created.

Masked - A texture property that uses the alpha channel to determine whether or not a section of the texture is transparent or opaque. Masked textures have no translucency. To use the Masked setting one must have the texture's bMasked property set to False.

Material - A tool used for creating special effects with textures. Materials show up and can be browsed in the texture browser and they are also saved in texture packages. For more on using the different types of Materials see the Texturing and Materials document.

Matinee - An in-editor keyframing tool that allows one to move objects and change properties in the game. You can also use it for camera paths and to create in-game cut scenes. For more information on using Matinee, see the Matinee User Guide document.

Max - (3DS Max) A 3rd party modeling program that can be used for creating intricate staticmeshes and/or skeletal meshes.

Maya - A 3rd party modeling program that can be used for creating intricate staticmeshes and/or skeletal meshes.

Mesh Emitter - An individual emitter that emits staticmeshes in a pattern that can be designed within the Unreal Editor. For more information on Mesh Emitters, see the Particle System Reference document.

Meshes - A model created in a 3rd party program that represents some entity; the term Mesh is often used interchangeably with the terms static mesh and skeletal mesh even though they are not the same thing.

Mod - User-created content that is largely based on another commercial game (such as Unreal Tournament) but is modified to create a different, or modified, game play experience.

Modifier - A material that can modify a texture or another material in a variety of ways including (but not limited to) allowing it to pan, waiver, rotate, and scale.

Mover - A special staticmesh that can be assigned keyframes within the editor and then assigned to move along a path determined by these keyframes when triggered by an event such as player collision, weapon fire, or a trigger.

Music - Song files that can be added to a level to be played in the background or Triggered after an event. These song files must be in the .ogg file format.

N & O

NonZeroExtentTraces - A trace that uses a box traveling along a line to determine collision. In other words, instead of using casting a 2 dimensional line to determine if a line can be drawn between two points, a 3 dimensional box is cast along a line to see what will impede the box.

Notifies - A call that can be placed at any point in a given animation that can trigger another event including but not limited to spawning sounds, particle systems, or executing UnrealScript functions. Foot steps sounds that are played when a foot reaches the ground in an walk animation are a good example of Notifies.

Novodex - The rigid body physics engine used in Unreal Engine 3 to simulate realistic movement and collision between objects. Novodex is also used by the vehicle system in UE3. Novodex is owned by Ageia, and have a web site at http://www.ageia.com. See PhysX.

Outer - For Objects stored in packages Outer is usually the group or package they are in. For those stored in the level the Outer is the level.

Order - See Sorting.


P8 - A palletized 8 bit texture.

Package - High-level data structure used as a container for UObjects. All UObjects contained within a package have that package as the value for its Outer property.

Particle System - See Emitter

Particle Emitter - An individual type of Emitter inside a Particle System (such as a Beam Emitter, Mesh Emitter, Spark Emitter, or Sprite Emitter. See Emitter

Pass - One time that the scene is drawn in the renderer. A scene can require several Passes by the renderer before it is drawn to the screen. In other words, if a triangle is requires 3 passes, it is being drawn 3 times by the renderer.

Path Node - A point in a network of lines that determine where a bot can travel to. Path Nodes appear as apples in the editor. For more information on Path Nodes, see the NavigationAI document.

Pawn - A character or class that can navigate (either on its own or by player control) through the level.

PhAT - The Physics Asset Tool, part of the Editor, which is used for creating PhysicsAssets. PhAT allows you to take a skeletal mesh, and assign collision shapes and joints to the bones. It also allows you to preview the physics setup in real time and interact with it. You can see more PhAT in the Physics Asset Tool(PhAT) document.

PhysicsAsset - A collection of collision shapes and joint setups which make up the physics information about a skeletal mesh. An example would be a ragdoll setup, but you can also use PhysicsAssets to represent the physics of any articulated object. PhysicsAssets are also used to update the bounding box of the skeletal mesh, and can be used for per-bone hit detection. PhAT is the tool used for creating Physics Assets.

PhysX - The physics engine by Ageia (formerly Novodex) which was integrated into Unreal Engine 3.

Play Map - Running the level in real time as the end user would be running the map.

Player - An actual human user of the map as it is running in real time. (they do exist!)

PlayerStart - A spawn point for a player's pawn or bot in the level.

Portal - (a.k.a. Zone Portal ) A particular type of special brush usually in the form of a sheet that can divide one zone into two different zones. For more information on Portals, see the LevelOptimization (BSP) document.

Poly - (a.k.a. Polygon ) A triangle.

Primitive - One of the standard, unaltered BSP shapes that can be created with the tools on the left side of the editor (i.e. cube, curved stair, cylinder, cone, sheet, etc.). For more information on Primitives, see the UnrealEd User Guide document.

Projector - An actor that can cast a texture on various types of geometry in the scene.

Properties - The settings for any actor or texture. To access the Properties of an actor, just press F4 or right click on the actor.

Q & R

Quad - A set of two triangles that make up a square, easily seen in terrain in wireframe mode.

Ragdoll - A realistic physics simulation applied to character models that allows them to act like limp ragdolls. For more information on how to set up the PhysicsAsset for a ragdolls, see the Physics Asset Tool(PhAT) document.

Rebuild - See Build

Refpose - ( Reference Pose ) The default position that an animated character is posed in before it is animated (usually the da Vinci pose).

Renderer - The part of the Unreal engine that actually draws what the player sees on the screen.

RGBA8 - a Red Green Blue 8 bit image.

Root - The primary bone at the top of the hierarchy of a skeletal animation. The Root is what is translated and/or rotated as a character moves through a level.

Rotation Gizmo - An interface for rotating and translating actors.

Rotation Grid - A toggle that allows one to rotate actors about its pivot point at discrete intervals. For more information on using the Rotation Grid, see the UnrealEd User Guide document.

Runtime - The mode when the level is actually running and one can interact as a player within the world.


Seamless Worlds - The seamless world system is aimed at dynamically background-loading and unloading the complex data associated with levels. This works in conjunction with streaming so that, together, all of the data associated with worlds may be dynamically loaded.

Script - See Unreal Script

Shadow depth buffer - A technique for rendering soft edged dynamic shadows. Unreal Engine 3 renders the shadows cast by dynamic objects from static lights using shadow depth buffers.

Shadow-map - A texture or per-vertex mask which stores a precomputed shadowing term for a specific light to each point on a mesh or BSP surface.

Shadow volume - A technique for rendering hard edged dynamic shadows. Unreal Engine 3 renders the shadows cast by dynamic light using shadow volumes.

Shape Editor - (a.k.a. 2D Shape Editor ) A tool in the Unreal Editor that allows one to create unique BSP brushes.

Sheet - A 2D brush often used for creating ZonePortals.

SimpleBoxCollision - A staticmesh collision type that uses NonZeroExtentTraces to calculate collision. For more information on SimpleBoxCollision, see the Collision Reference document.

SimpleRigidBodyCollision - A staticmesh collision type that uses Hulls to calculate rigid-body collisions. For more information on SimpleRigidBodyCollision, see the Collision Reference document.

SimpleLineCollision - A staticmesh collision type that uses ZeroExtentTraces to calculate collision. For more information on SimpleLineCollision, see the CollisionReference document.

Skeletal Mesh - A mesh that can be animated using a skeleton and animations created in a 3rd party modeling program. For more information on setting a Skeletal Mesh, see the Importing Skeletal Meshes Tutorial document.

Skeleton - The bones set up in a 3rd party modeling program for an animated character.

Skin - The texture(s) applied to a mesh (staticmesh, skeletal mesh, etc.)

Skins Array - A field in the properties window that allows one to switch in different skins or textures onto a model.

Sky Dome - A large hemisphere static-mesh which is used to create the illusion of a far off sky. See SkyZone.

Snap - (Referring to Gird Snap ) A feature that aligns geometry to the grid whenever it is moved or rotated.

Socket - A named attachment point on a bone of a skeletal mesh. You can see more info on setting up and using socket in the SkeletalMeshSockets document.

Sorting - Choosing the order or hierarchy of what the renderer will draw first.

Special Brush - A brush that is added through use of the Add Special Brush button that allows for not only a pull down selection of possible default Special Brushes as well as customizing a unique Special Brush. For more information on Specail Brushes, see the UnrealEd User Guide document.

Sprite - A texture applied to a plane (usually used with particle systems).

Sprite Emitter - An individual emitter that emits sprites in a pattern that can be designed within the Unreal Editor. For more information on Sprite Emitters, see the Particle System Reference document.

StaticMesh - (a.k.a. Static Mesh ) A model created in a 3rd party program that remains stationary in the level when added to a map.

Streaming - (a.k.a. Content Streaming) A mechanism to load large amounts game and scene information on demand from source media. This is beneficial on consoles or other machines where it is not possible to store the entire scene in memory at once. Levels, textures and other types of data may be streamed.

Subobject - Object contained within another object, (with the exception of UObjects contained within packages). Subobjects are normally declared in the defaultproperties block of a class's .uc file, using a 'Begin Object/End Object' syntax.

Subtractive BSP - BSP Space that has been subtracted from the solid and/or additive world space. Subtractive BSP is open space in the level that the players can walk around in. See BSP.

Surface - The visible texture of BSP.

Surface Properties - The attributes that can be assigned to a BSP surface. For more information on Surface Properties, see the UnrealEd User Guide document.


Tag - The name given to a specific actor in the world under the events tab in the actor's properties window.

Targa - A file format for textures that the Unreal Engine can import.

Teleporter - An actor that can instantly send a player from one point in the map to any other point in the map or even a point in another map.

Template - A suboject contained within a class default object.

Terrain - (a.k.a. TerrainInfo ) A type of geometry in the form of a heavily tessellated sheet than can be deformed and sculpted using the Terrain Editor tool within the Unreal Editor. For more information on using Terrain, see the Terrain Editor User Guide document.

Terrain Layer - Hierarchical levels in the Terrain that allow Textures to be painted on and blended together on the terrain. For more on Layers, see the Setting up Terrain] document.

Texture - An image file that can be assigned to geometry in the world. Materials are also sometimes referred to as Textures. For more information on Textures, see the Texturing and Materials document.

Trace - A line (for calculation purposes only) drawn from one point to another (such as from a gun to a target) that is used for determining collision.

Triangle - The smallest renderable building block of world geometry out of which everything in the scene is constructed.

Trigger - An actor that can activate an event during game play.


UnEdit3 - A mailing list available to all Unreal Engine 3 licenses that functions as a support group for Unreal Engine content creation and working with the Unreal editor. For more information about UnEdit, see the UnEdit3 document.

Unreal Developer Network - (a.k.a. UDN )The team that supports the licensees of the Unreal Engine. For more information on the Unreal Developer Network, see the Main.WebHome page.

UnrealEd - (a.k.a. Unreal Editor ) The editing tool that allows one to create playable interactive worlds.

UnrealScript - A simple coding language native to Unreal that can be used for creating scripted sequences (a series of actions) for AI as well as game events.

URU - (a.k.a. Unreal Rotation Unit; Unreal Unit) The unit of measure for units over distance or rotation in Unreal Ed. Note that in Unreal Rotation Units 16384 = 90?

UT - (a.k.a. Unreal Tournament) One of the titles released using a first generation build of the Unreal Engine. To see other first generation release titles, see the Powered.FirstGenerationTitles document.

UT2003 - (a.k.a. Unreal Tournament 2003) a released title based on a heavily modified Unreal engine build 2110. For more information on UT2003, see the Powered.UnrealTournament2003 page.


Vertex - ( plural Vertices ) One point of a geometry triangle

Vertex Color - A technique for tinting geometry by adding color based on vertices.

Viewport - A display window in the Unreal Editor that can show a front, side, top, or perspective views. For more information on Virewports, see the UnrealEd User Guide document.

Volume - A 3D space that can effect various game play features such as movement, visibility, and player damage.


WarpZone - A special zone that contains a WarpZoneInfo that allows players to instantly travel from that WarpZone to another corresponding WarpZone.

Wiki - A webpage formatting system that allows for easy and fast online maintenance. The UDN website is Wiki based.

Wiki wiki - Hawaiian for Fast.

World - (See Map, Levels) The construct which forms the entire scene in the game. Worlds in Unreal Engine 3 may consist of many smaller constructs known as levels. Worlds are stored in map files.

X, Y & Z

Zone - An area in the level that is sectioned off by portals for optimization purposes. For more information on Zones, see the Level Optimization (BSP) document.

ZoneInfo - An actor that allows one to alter the properties of the Zone within which it resides.

ZBuffer - The section of video memory in a graphics card that keeps track of which onscreen elements can be viewed and which are hidden behind other objects.

ZeroExtentTraces - A trace that uses a 1 dimensional line traveling between a source and a target to determine collision.

ZFight - A flickery visual artifact that occurs when two surface either occupy the same plane space or are very close to occupying the same plane and space where the visible textures appear to "fight" for visual dominance.

Zone Portal - See Portal