Just as with variable values, Blueprints can store data within Arrays. If you are not versed in programming terms, you can think of an Array as a collection of variables all housed within a single unit.
An Array can only hold values of a single type. For instance, a Boolean Array can only hold Boolean values.
Array variables will contain a 3x3 colored grid to show that they are Arrays and not regular variables. In the case of a disconnected Array, that grid will have a darkened center. Once connected, the entire grid will be visible, as seen below.