Bounding volume
A simple shape that fully encloses a complex object, letting a cheap test reject it before the expensive one ever runs.
A bounding volume is a simple shape — box, sphere, capsule or k-DOP — that completely contains a detailed mesh. The whole point is cheap rejection: if two volumes don't overlap, the geometry inside them can't either, so the expensive test is skipped.
The trade-off is tightness against test cost. A sphere is cheapest to test but wraps loosely; an OBB fits snugly but costs more. AABB sits in between and dominates the broad phase because its overlap test is just interval comparisons. Volumes nest into a BVH for logarithmic culling, and the same idea underpins frustum culling and ray-tracing acceleration structures.