A key is an instrument used to unlock a lock. In most cases, this lock is a door lock.

The key is inserted into a keyhole and then turned. The use of keys is a very traditional method of access control and property protection (keys already existed in ancient times) and is still widely used today. While keys were originally made of wood, today almost all keys are made from various types of metal.

There are numerous key variants and types in circulation. For example, there are master keys or bump keys (bump keys are recognizable by their cut profile). In general, the range of key types is very diverse.