A lock is a mechanical or electronic fastening device that is released by a physical object (such as a key, keycard, fingerprint, RFID card, security token, coin etc.), by supplying secret information (such as a number or letter permutation or password), or by a combination thereof or only being able to be opened from one side such as a door chain.
A lock may also be a clamp or a stop designed to prevent the flow of a liquid or the motion of a caster or wheel