Secret Key

A cryptographic key that is used with a secret-key (symmetric) cryptographic algorithm that is uniquely associated with one or more entities and is not made public. The use of the term “secret” in this context does not imply a classification level, but rather implies the need to protect the key from disclosure.
SOURCE: SP 800-57 Part 1

A cryptographic key that is used with a symmetric cryptographic algorithm that is uniquely associated with one or more entities and is not made public. The use of the term “secret” in this context does not imply a classification level, but rather implies the need to protect the key from disclosure.
SOURCE: CNSSI-4009

A cryptographic key that must be protected from unauthorized disclosure to protect data encrypted with the key. The use of the term “secret” in this context does not imply a classification level; rather, the term implies the need to protect the key from disclosure or substitution.
SOURCE: FIPS 201

A cryptographic key that is uniquely associated with one or more entities. The use of the term “secret” in this context does not imply a classification level, but rather implies the need to protect the key from disclosure or substitution.
SOURCE: FIPS 198

A cryptographic key, used with a secret key cryptographic algorithm, that is uniquely associated with one or more entities and should not be made public.
SOURCE: FIPS 140-2