Slide bearings or plain, bearings encompass a range of mechanical components that go by various names but are generally grouped as fluid-film bearings, whose purpose is to reduce friction between rotating, reciprocating, or sliding surfaces such as shafts and stationary surfaces such as housings. The lubricating film is generally oil, although water is sometimes used in special situations, and “dry Running” bearings attain their slipperiness by way of PTFE or other low-friction materials. Slide bearings differ from ball and roller bearings which use rolling elements to reduce friction but in both instances, the goal is the same.
These machine elements go by many names, including sleeve bearings, bushings, journal bearings, sliding bearings, friction bearings, etc. They were in use long before practical ball and roller bearings were developed.