A plain bearing, or more commonly sliding bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing), is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore, the journal (i.e., the part of the shaft in contact with the bearing) slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests on or the ways on the bed of a lathe.Plain bearings are used in many industries and across many applications where there is a need to cost-efficiently and reliably meet the challenge of oscillating movements and possible misalignment. From mining and construction equipment, farm and forestry machinery, all the way to forklift trucks and solar power equipment.

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.