A Directional Light simulates light that is being emitted from an infinitely large source that is infinitely far away. This means that all shadows cast by this light will be parallel, making this the ideal choice for simulating sunlight. The only visible indicator on a Directional Light is a 3D arrow which points in the direction the light will travel.
In this example, the Directional Light is coming through a hole in the ceiling. Since a Directional Light is calculated as being infinitely far away, its location is irrelevant. Only its rotation is used to determine the light's angle.