Anatomy of a Rolling Element Bearing
A rolling element bearing (which is a type of anti-friction bearing) involves the motion of two surfaces separated either by rollers or balls (the rolling elements) whose primary purpose is to reduce friction. The typical rolling element bearing will consist of
(a) an inner race,
(b) an outer race (which together form the raceway),
(c) the rolling elements between them, and
(d) usually some type of cage (also known as a separator or retainer) to hold the rolling elements in place and prevent them from contacting each other.
The only kind of rolling element bearing that does not have a cage is a called a full complement bearing. The inner and outer race will have a groove in them, in which the rolling elements rest.
Here are some additional excellent posts on bearings and bushings from Advanced EMC Technologies: