A key is an object used to open and close locks. Many things have locks, for example, doors. Keys are also used to turn on cars, machines and other things.

A key is used by placing the key into the slot of the thing you want to unlock.

A key that can open more than one lock (if each lock also has its own key) is called a master key or skeleton key.

A key is an object used to open and close locks. Many things have locks, for example, doors. Keys are also used to turn on cars, machines and other things. A key is used by placing the key into the slot of the thing you want to unlock. A key that can open more than one lock (if each lock also has its own key) is called a master key or skeleton key.