Seals, Bearings and Hub assemblies: A wheel bearing on a car is a set of ball bearings that support the wheel and ride on a metal shaft which is called an axle shaft. The wheel bearing is located at the hub, the hub is located at the center of your wheel, when you are looking at a wheel on a car, the hub is located where the lug bolts come through the wheel. The lug bolts are pressed into the hub, and the wheel bearing is pressed into the hub as well, from the back side of the hub.
Wheel bearings are used on all types of vehicles and they all perform the same job, They allow the wheel to spin freely. A wheel bearings worst two enemies are heat and water. Heat is caused by the lack of lubrication which can destroy a wheel bearing, and water that penetrates the sealed bearing will the destroy the wheel bearing as well.
A tell tale sign of a damaged wheel bearing is noise, and it will only get louder with time and the only remedy is replacement.