Definition
A mechanical bearing made up of an inner race, an outer race, a set of hardened steel balls held between the races, and a cage (or separator) that keeps the balls evenly spaced. The balls roll between the two races, allowing one race to rotate freely relative to the other while supporting radial loads, and in many designs, a degree of axial (thrust) load.
Plain English
A bearing that uses small steel balls trapped between two rings so a shaft can spin smoothly with very little friction. The balls roll instead of slide, which is why the motion is so easy.
Context Anchor
Seen in aircraft maintenance when inspecting or replacing rotating parts such as wheels, pulleys, alternators, starters, and control-system components.
Derivation
The name describes the parts: 'ball' for the rolling spheres, and 'bearing' from an old engineering use meaning 'the part that bears (carries) the load.' So a ball bearing assembly is literally an assembled load-carrying part that uses balls to do the carrying.
Why Pilots Care
A failed ball bearing assembly creates friction and heat that can seize rotating parts, damage engines, or cause wheel lockup on landing.
Intuition Check
Do not picture loose metal balls by themselves. A ball bearing assembly is the complete bearing unit that holds the balls in the correct place so a part can rotate smoothly.
Example Sentence 1
The mechanic replaced the ball bearing assembly in the nose wheel after noticing roughness during the last inspection.
Example Sentence 2
During the annual inspection the technician checked the main wheel ball bearing assembly for play and roughness.