Key Derivation Function.
Source(s):
NIST SP 800-108 under KDF

  A function that, with the input of a cryptographic key and other data, generates a binary string, called keying material.
Source(s):
NIST SP 800-108 under Key derivation function

  A function by which keying material is derived from a shared secret (or a key) and other information.
Source(s):
NIST SP 800-56A Rev. 2 [Superseded]

  A function that, with the input of a cryptographic key or shared secret, and possibly other data, generates a binary string, called keying material.
Source(s):
NIST SP 800-57 Part 1 Rev. 4 [Superseded]
NIST SP 800-57 Part 1 Rev. 3 [Superseded]

  As used in this Recommendation, a function used to derive secret keying material from a shared secret (or a key) and other information.
Source(s):
NIST SP 800-56B Rev. 2

  A function that − with the input of a cryptographic key or shared secret and possibly other data − generates a binary string, called keying material.
Source(s):
NIST SP 800-57 Part 1 Rev. 5

  As used in this Recommendation, either a one-step key-derivation method or a key-derivation function based on a pseudorandom function as specified in SP 800-108.
Source(s):
NIST SP 800-133 Rev. 2

  A function used to derive keying material from a shared secret (or a key) and other information.
Source(s):
NIST SP 800-56B Rev. 1 [Superseded]