Plain bearings are mechanical components charged with bearing a load and allowing a sliding or rotational motion between two parts of a machine. Their main purpose is preventing wear of the points of support of the machine, which would take place if the shafts were to roll directly on the structure.

The use of bearings, simplistic as they may have been then, dates back to at least the ancient Egyptians, and perhaps even predated the invention of the wheel. Today bearings can be found wherever there is relative motion between two surfaces, which includes virtually everything from household appliances to industrial machinery.