Collider
The invisible, simplified shape — box, sphere, capsule or mesh — a physics engine uses to detect contact, almost always coarser than the visible model.
A character may carry ten thousand triangles in its visible mesh but a single capsule as its collider, because physics can never afford to test every triangle. Primitive colliders (box, sphere, capsule) are cheap; convex hulls and mesh colliders are expensive and occasionally unreliable. Unity and Godot use the term verbatim.
A collider can be solid or a trigger that merely reports overlap without stopping anything — the basis for pickups and zones. Several colliders can be assembled into a compound shape when a single primitive won't do.