For locks on a river or canal, see Lock (water transport)

A padlock

A lock and two latches on a trunk

An electronic lock on a door

A lock keeps things closed. It keeps people from opening something, such as a door or a box. Keys open locks. Sometimes an electronic card or secret numbers will open a lock. The verb to lock means to set the lock so the door or object is closed. A person who works on locks is called a locksmith.