X.509 v3 certificate (n)~ A certificate that adheres to the syntax and format described in version 3 of the International Telecommunication Union - Telecommunication [Standardization Sector] (ITU-T) recommendation X.509. This is the standard certificate format used by Windows certificate-based processes. An X.509 certificate includes the public key and information about the person or entity to whom the certificate is issued information about the certificate plus optional information about the certification authority (CA) issuing the certificate.