Bounding box / bounding sphere
An invisible box or sphere wrapped around a detailed object so visibility, picking, and possible collisions can be checked cheaply.
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What it is
A bounding volume is a simple shape wrapped around a more complicated object. An axis-aligned bounding box, or AABB, stores minimum and maximum coordinates along the world axes. A bounding sphere stores a center and radius. Testing either one is far cheaper than testing every triangle in the mesh.
Bounds are the first question in frustum culling, picking, broad-phase collision detection, and spatial indexes: could these objects possibly touch or be visible? Boxes fit rectangular objects more tightly; spheres are rotation-invariant and especially cheap. A game's hitbox is the same idea aimed at gameplay rather than rendering. An oriented bounding box fits rotated objects better but costs more to update and test.
Gotcha: a bounding-volume hit is only a maybe. Empty corners of a box and empty space inside a sphere create false positives, so precise interactions need a second narrow-phase test. Bounds also go stale when vertices move, instances spread out, or transforms change without an update.
Ask AI for it
Add broad-phase bounds to this three.js scene. Build a THREE.Box3 for each static mesh with Box3.setFromObject(), derive a THREE.Sphere from the box, and show both through Box3Helper plus a wireframe sphere debug mesh. Update dynamic bounds after world matrices change, use Box3.intersectsBox() to find possible collision pairs, then run the existing triangle-level test only for those pairs. Color false-positive box hits amber and confirmed narrow-phase hits red.