- a bearing in which the moving parts revolve or slide on freely rolling metal balls so that friction is reduced
- any of such metal balls
- A friction-reducing bearing consisting essentially of a ring-shaped track containing freely revolving hard metal balls against which a rotating shaft or other part turns.
- A hard ball used in such a bearing.
- A ring-shaped track containing hard metal balls that roll freely, used to reduce friction where a rotating element (such as an axle) is attached to a fixed point.
- A hard ball used in such a track.