The party that provides assurance to the other party (the recipient) that the two parties have indeed established a shared secret or shared keying material.
Sources:
NIST SP 800-56B Rev. 2
The party that provides assurance to the other party (i.e., the recipient) that the two parties have indeed established a shared secret key or other keying material.
Sources:
NIST SP 800-227
under key-confirmation provider