AABB
A bounding box whose edges run parallel to the coordinate axes, so it is described by nothing more than a minimum and a maximum value per axis.
The name stands for axis-aligned bounding box. Its virtue is that the overlap test collapses to trivial comparisons: two boxes intersect only if their intervals overlap on every axis at once. That makes the AABB the obvious cheap proxy in a broad phase, before the expensive exact geometry gets tested in narrow phase.
The catch is that the box does not rotate with the object — turn the model and the AABB must be rebuilt, and it also loosens, leaving slack air in the corners. For a tighter fit you reach for an OBB (oriented box), paying with a fiddlier test. For objects moving between frames, a swept AABB sweeps the box along its path instead.