A thrust bearing is a particular type of rotary bearing. Like other bearings they permit rotation between parts, but they are designed to support a predominately axial load.
Thrust bearings are commonly used in automotive, marine, and aerospace applications. They are also used in the main and tail rotor blade grips of RC (radio controlled) helicopters.
Thrust bearings are used in cars because the forward gears in modern car gearboxes use helical gears which, while aiding in smoothness and noise reduction, cause axial forces that need to be dealt with.