The Free On-line Dictionary of Computing (30 December 2018):

Certificate Authority

    (CA or "Trusted Third Party") An entity
   (typically a company) that issues digital certificates to
   other entities (organisations or individuals) to allow them to
   prove their identity to others.  A Certificate Authority might
   be an external company such as VeriSign that offers digital
   certificate services or they might be an internal organisation
   such as a corporate MIS department.  The Certificate
   Authority's chief function is to verify the identity of
   entities and issue digital certificates attesting to that
   identity.

   The process uses public key cryptography to create a
   "network of trust".  If I want to prove my identity to you, I
   ask a CA (who you trust to have verified my identity) to
   encrypt a hash of my signed key with their private key.
   Then you can use the CA's public key to decrypt the hash and
   compare it with a hash you calculate yourself.  Hashes are
   used to decrease the amount of data that needs to be
   transmitted.  The hash function must be cryptographically
   strong, e.g. MD5.


(http://home.netscape.com/comprod/server_central/support/faq/certificate_faq.html#11).

   (1998-03-30)