Key, code, or authentication information in physical, electronic, or magnetic form. It includes key tapes and list, codes, authenticators, one-time pads, floppy disks, and magnetic tapes containing keys, plugs, keyed microcircuits, electronically generated key, etc.
Sources:
CNSSI 4009-2015 from CNSSI 4005

  A bit string, such that any non-overlapping segments of the string with the required lengths can be used as symmetric cryptographic keys and secret parameters, such as initialization vectors.
Sources:
NIST SP 800-107 Rev. 1 under Keying Material

  Data that is represented as a binary string such that any non-overlapping segments of the string with the required lengths can be used as secret keys, secret initialization vectors and other secret parameters.
Sources:
NIST SP 800-56B Rev. 2 under Keying material

  A cryptographic key and other parameters (e.g., IVs or domain parameters) used with a cryptographic algorithm.
Sources:
NIST SP 800-57 Part 1 Rev. 5 under Keying material
NIST SP 800-57 Part 2 Rev.1 under Keying material

  A cryptographic key and other parameters (e.g., IVs or domain parameters) used with a cryptographic algorithm. When keying material is derived as specified in SP 800-56CSP 800-108:bit string such that any non-overlapping segments of the string with the required lengths 4 and 5 Data represented as a can be used as secret keys, secret initialization vectors, and other secret parameters.
Sources:
NIST SP 800-175B Rev. 1 under Keying material

  A bit string such that non-overlapping segments of the string (with the required lengths) can be used as cryptographic keys or other secret (pseudorandom) parameters.
Sources:
NIST SP 800-108r1 [August 2022 (Includes updates as of 02-02-2024)]

  Data that is represented as a binary string such that any non-overlapping segments of the string with the required lengths can be used as secret keys, secret initialization vectors, and other secret parameters.
Sources:
NIST SP 800-56C Rev. 2 under Keying material