A freewheel is a ratchet mechanism mounted on the rear hub which allows the chain to drive the wheel forwards via a cog but when the wheels move faster than the chain the cog is not driven round by the wheel. A freewheel allows a rider to rest their legs while the bike is moving forward.
Engage the bike freewheel
Lift the rear wheel of the ground and kick the pedals to start it turning.
The rear wheel should spin while the cranks stop turning. If the rear wheel pushes the cranks around there may be a problem with the bike freewheel.
The bike freewheel should make a regular metallic clicking sound when the wheel runs and the pedals are still. Changes in the sound of a bike freewheel may be a sign that it’s wearing out.