Cryptographic Key

A value used to control cryptographic operations, such as decryption, encryption, signature generation, or signature verification.
SOURCE: SP 800-63

A binary string used as a secret parameter by a cryptographic algorithm.
SOURCE: SP 800-108

A parameter used in conjunction with a cryptographic algorithm that determines the specific operation of that algorithm.
SOURCE: FIPS 201; FIPS 198

A parameter used in conjunction with a cryptographic algorithm that determines

• the transformation of plaintext data into ciphertext data,
• the transformation of ciphertext data into plaintext data,
• a digital signature computed from data,
• the verification of a digital signature computed from data,
• an authentication code computed from data, or
• an exchange agreement of a shared secret.

SOURCE: FIPS 140-2