A ball bearing is a common type of rolling-element bearing, a kind of bearing. The term ball bearing to mechanical engineers usually means a bearing assembly which uses spherical bearing balls as the rolling elements. To laypeople the term often means an individual ball for a bearing assembly. The remainder of this entry uses the term ball for the individual component and "ball bearing" or just "bearing" for the assembly. Ball bearings typically support both axial and radial loads and can tolerate some misalignment of the inner and outer races. Also, balls are relatively easy to make cheaply compared to other kinds of rolling elements. Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area that spherical shapes provide. (wikipedia)