k-DOP
A bounding volume shaped by k half-spaces with fixed normal directions — tighter than an AABB, cheaper to test than the real hull.
An axis-aligned box (AABB) is free to test but often wastes space around slanted objects. A k-DOP (discrete oriented polytope) shaves off the corners with k predefined planes: a 6-DOP is just the AABB, a 14-DOP adds the four cube diagonals, 18- and 26-DOP add still more.
Because the normals are shared across every object, the overlap test reduces to k interval comparisons — nearly as cheap as an AABB but with a far tighter fit. It is popular as the node volume in a BVH, where the tighter bound cuts false hits deeper in the tree.