A procedure in which a new cryptographic key is generated in a manner that is independent of the (old) cryptographic key that it will replace.
Sources:
NIST SP 800-133 Rev. 2
To change the value of a cryptographic key that is being used in a cryptographic system application; this normally entails issuing a new certificate on the new public key. NIST SP 800-32 under Re-key (a certificate)
Sources:
NIST SP 1800-16C