Real Dictionary

ball bearing
countable noun: Ball bearings are small metal balls placed between the moving parts of a machine to make the parts move smoothly.

ball bearing in American English
a bearing in which the moving parts revolve or slide on freely rolling metal balls so that friction is reduced
noun: a bearing consisting of a number of hard balls running in grooves in the surfaces of two concentric rings, one of which is mounted on a rotating or oscillating shaft or the like

ball bearing in British English
noun: a bearing consisting of a number of hard steel balls rolling between a metal sleeve fitted over the rotating shaft and an outer sleeve held in the bearing housing, so reducing friction between moving parts while providing support for the shaft

ball bearing in Mechanical Engineering
noun: A ball bearing is a bearing containing hard steel balls.