A plain bearing, or more commonly sliding bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing[citation needed]), 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, in general, are the least expensive type of bearing. They are also compact and lightweight, and they have a high load-carrying capacity.

The design of a plain bearing depends on the type of motion the bearing must provide. The three types of motions possible are:
Journal (friction, radial or rotary) bearing: This is the most common type of plain bearing; it is simply a shaft rotating in a bearing. In locomotive and railroad car applications a journal bearing specifically referred to the plain bearing once used at the ends of the axles of railroad wheel sets, enclosed by journal boxes (axleboxes). Axlebox bearings today are rolling-element bearings rather than plain bearings.
Linear bearing: This bearing provides linear motion; it may take the form of a circular bearing and shaft or any other two mating surfaces (e.g., a slide plate).
Thrust bearing: A thrust bearing provides a bearing surface for forces acting axial to the shaft. One example is a propeller shaft.