Master Key (Mk) definition in Computer Security terms:
Definition(s): In this Recommendation, a master key is the keying material that is output from an execution of the PBKDF.
Source(s): NIST SP 800-132
In this Recommendation, the master key refers to the keying material derived by participating parties upon successfully completing a key establishment protocol. The derived keying material may be used to derive further keys.
Source(s): NIST SP 800-120
Synonym(s): Key-Derivation Key
A key used as an input to a key-derivation method to derive other keys.
Source(s): NIST SP 800-133 A key that is used as an input to a key derivation function or key expansion function to derive other keys.
Source(s): NIST SP 800-135 Rev. 1 A key used with a key-derivation function or method to derive additional keys. Also called a master key.
Source(s): NIST SP 800-57 Part 1 Rev. 3
reference: CSRC Glossary