A bearing (bushing) is a sliding and lubricating structure in order to decrease friction between different moving parts (rotating or sliding).
A ball bearing is a rolling bearing that does this for a spinning motion. It consists of an inner ring and an outer ring separated by one or two rows of spherical, cylindrical or barrel-shaped bullets.
A ball bearing is mainly used to connect the axle with the hub of a wheel. You can find them e.g. in bike wheels, but also in the bottom bracket and the steering shaft.
If a metal ball bearing has too little fat or lubricating oil, the bearing can jam by the heat generated by the friction. With respect to each other the balls rotate in opposite directions. Do not too much fat in the bearing, he may only be filled two thirds otherwise the fat rotates. As a result, it heats and melts, and runs out of the bearing.

My very elderly former neighbor blessed smeared his wooden wheelbarrow wheel regularly with a finger soft brown soap.

"Without the invention of the wheel, the riders in the Tour de France would have to travel with their bikes on their backs. “ (Pierre Dac)