n. pl. keys 1. a. A notched and grooved, usually metal implement that is turned to open or close a lock.
b. A similar implement or an electronic device used for opening, winding, or starting something: the key of a wind-up alarm clock; the new car's electronic key.
c. A device, such as a wedge or pin, inserted to lock together mechanical or structural parts.
d. A keycard.
2. A determining factor in accomplishing or achieving something: One key to the store's success has been consistent customer service.
3. a. Something that provides access to or understanding of something else: The key to the mystery was a drug store receipt.
b. A set of answers to a test.
c. A table, gloss, or cipher containing correspondences, as for decoding or interpreting something.
d. Computers A number used by a cryptographic algorithm to encrypt or decrypt data.
4. Architecture The keystone in the crown of an arch.
5. a. A button or lever that is depressed to operate a machine.
b. A button that is depressed to cause a corresponding character or function to be typed or executed by a typewriter or to be accepted as input by a computer.
c. Music A button or lever that is depressed with the finger to produce or modulate the sound of an instrument, such as a clarinet or piano.
6. Music a. A tonal system consisting of seven tones in fixed relationship to a tonic, having a characteristic key signature and being the structural foundation of the bulk of Western music; tonality.
b. The principal tonality of a work: an etude in the key of E.
7. The pitch of a voice or other sound.
8. A characteristic tone or level of intensity, as of a speech or sales campaign. Often used in combination: high-key; low-key.
9. Botany A samara.
10. An outline of the distinguishing characteristics of a group of organisms, used as a guide in taxonomic identification.
11. Basketball An area at each end of the court between the baseline and the foul line and including the jump-ball circle at the foul line: a jump shot from the top of the key.
12. The act of replacing portions of a video or photograph containing a preselected color with material from a separate image, as by chroma key.