A certificate signing request (also CSR or certification request) is a message sent from an applicant to a certificate authority of the public key infrastructure in order to apply for a digital identity certificate.
It usually contains the public key for which the certificate should be issued, identifying information (such as a domain name) and a proof of authenticity including integrity protection (e.g., a digital signature).
The most common format for CSRs is the PKCS #10 specification.