A request sent from a certificate requester to a certificate authority to apply for a digital identity certificate. The certificate signing request contains the public key as well as other information to be included in the certificate and is signed by the private key corresponding to the public key.
Sources:
NIST SP 1800-16B
under Certificate Signing Request
NIST SP 1800-16C
under Certificate Signing Request
NIST SP 1800-16D
under Certificate Signing Request