The freewheel is a ratcheting mechanism, that coupled with a set of gears, is that threaded onto the rear hub of a bike. The freewheel allows the rear wheel to engage and move when the pedals are spun forward, but coast freely when the pedals are stationary or spun backwards.
I heard an interesting opinion yesterday that said all freewheels made back in the day (we were discussing this over a wheel with a Maillard hub and a Maeda (?) freewheel). The shop mechanic said that ...