X.509 public key certificate definition in Computer Security terms:
Definition(s): The public key for a user (or device) and a name for the user (or device), together with some other information, rendered unforgeable by the digital signature of the certification authority that issued the certificate, encoded in the format defined in the ISO/ITU-T X.509 standard.
Also known as X.509 Certificate.
Source(s): CNSSI 4009-2015 (Adapted from NIST SP 800-57 Part 1 Rev. 3)
Synonym(s): X.509 certificate
The X.509 public-key certificate or the X.509 attribute certificate, as defined by the ISO/ITU-T X.509 standard. Most commonly (including in this document), an X.509 certificate refers to the X.509 public-key certificate.
Source(s): NIST SP 800-57 Part 1 Rev. 3 Public key certificates that contain three nested elements: 1) the tamper-evident envelope (digitally signed by the source), 2) the basic certificate content (e.g., identifying information and public key), and 3) extensions that contain optional certificate information.
Source(s): NIST SP 800-57 Part 2
reference: CSRC Glossary