1. In a public switched telecommunications network, the ultimate user, i.e., customer, of a communications service. Note 1: Subscribers include individuals, activities, organizations, etc. Note 2: Subscribers use end instruments, such as telephones, modems, facsimile machines, computers, and remote terminals, that are connected to a central office. Note 3: Subscribers are usually subject to tariff. Note 4: Subscribers do not include communications systems operating personnel except for their personal terminals. 2. In cryptography, a party that has a keying relationship with a center or an entity that has a certificate from a certification authority.