<database> A relational database key which depends wholly on one or more other columns in the same table. An intelligent key might be identified for implementation convenience, where there is no good candidate key. For example, if the three-letter initials of a group of people are known to be unique but only their full names are recorded, a three letter acronym for their names (e.g. John Doe Smith -> JDS) would be an intelligent key. Intelligent keys are a Bad Thing because it is hard to guarantee uniqueness, and if the value on which an intelligent key depends changes then the key must either stay the same, creating an inconsistency within the containing table, or change, requiring changes to all other tables in which it appears as a foreign key. The correct solution is to use a surrogate key. (1999-12-07)

A smart key is an electronic access and authorization system that is available either as standard equipment, or as an option in several car designs. It was first developed by Siemens in 1995 and introduced by Mercedes-Benz under the name "Keyless-Go" in 1998 on the W220 S-Class, after the design patent was filed by Daimler-Benz on May 17, 1997.

In music theory, the key of a piece is the group of pitches, or scale, that forms the basis of a musical composition in classical, Western art, and Western pop music.