A key is an instrument that is used to operate a lock. A typical key consists of two parts: the blade, which slides into the keyway of the lock and distinguishes between different keys, and the bow, which is left protruding so that torque can be applied by the user. The blade is usually intended to operate one specific lock or a small number of locks that are keyed alike. The key serves as a security token for access to the locked area; only persons having the correct key can open the lock and gain access.

Keys provide an inexpensive, though imperfect, method of access control for access to physical properties like buildings and vehicles. As such, keys are an essential feature of modern living in the developed world, and are common around the globe. It is common for people to carry the set of keys they need for their daily activities around with them, often linked by a keyring adorned by trinkets usually known as a keychain.

A house key is the most common sort of key. There are two main forms. The older form is for lever locks, where a pack of flat levers (typically between two and five) are raised to different heights by the key whereupon the slots or gates of the levers line up and permit a bolt to move back and forth, opening or closing the lock. The teeth or bittings of the key have flat tops rather than being pointed. Lever lock keys tend to be bigger and less convenient for carrying, although lever locks tend to be more secure.

Key may refer to:

"Medicine man" or "medicine woman" are English terms used to describe traditional healers and spiritual leaders among Native American and other indigenous or aboriginal peoples. Anthropologists tend to prefer the term "shaman," a specific term for a spiritual mediator from the Tungusic peoples of Siberia.

The primary function of these "medicine elders" (who are not always male) is to secure the help of the spirit world, including the Great Spirit (Wakan Tanka in the language of the Lakota Sioux), for the benefit of the entire community.

Sometimes the help sought may be for the sake of healing disease, sometimes it may be for the sake of healing the psyche, sometimes the goal is to promote harmony between human groups or between humans & nature. So the term "medicine man/woman" is not entirely inappropriate, but it greatly oversimplifies and also skews the depiction of the people whose role in society complements that of the chief. These people are not the Native American equivalent of the Chinese "barefoot doctors", herbalists, nor of the emergency medical technicians who ride rescue vehicles.