An air bearing is a bearing that literally consists of a layer of atmospheric air. Air bearings are often used where the gap between moving surfaces must be small and where differential velocity is high enough to allow the viscosity of air to build up enough pressure to keep the moving surfaces separated.
Examples of the use of an air bearing is the "flying head" in a computer's hard disk drive. Air bearings with compliant spring foil to maintain journal clearances are called foil bearings.