Roller Bearings are a type of rolling-element bearing, which uses cylinders (rollers) to maintain the separation between the moving parts of the bearing (as opposed to using balls as the rolling element).
The purpose of a roller bearing is to reduce rotational friction and support radial and axial loads. Compared to ball bearings, roller bearings can support heavy radial loads and limited axial loads (parallel to the shaft). They can operate at moderate to high speeds (although maximum speeds are typically below the highest speeds of ball bearings). The lubrication method must carefully considered during the design phase when using roller bearings.