A box approximation of an object used for collision & hit detection.
Axial-aligned Bounding Box stands for a 3D volume relative to a given origin. Effectively it is a cuboid which is not rotated. All of its edges are parallel to the axes it is alligned to.
Oriented Bounding Box stands for a 3D volume relative to a given origin and angle.
In many applications the bounding box is aligned with the axes of the co-ordinate system, and it is then known as an AABB. To distinguish the general case from an AABB, an arbitrary bounding box is sometimes called an OBB. AABBs are much simpler to test for intersection than OBBs, but have the disadvantage that when the model is rotated they cannot be simply rotated with it, but need to be recomputed.