Wiktionary
certificate authority
n. (context computing English) an organization which issues digital certificates for use by other parties
Wikipedia
Certificate authority
In cryptography, a certificate authority or certification authority (CA) is an entity that issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. This allows others (relying parties) to rely upon signatures or on assertions made about the private key that corresponds to the certified public key. In this model of trust relationships, a CA is a trusted third party—trusted both by the subject (owner) of the certificate and by the party relying upon the certificate. Many public-key infrastructure (PKI) schemes feature CAs.