An optical system in which the optical axis of the aperture is not coincident with the mechanical center of the aperture.
Note: The principal applications of off-axis optical systems are to avoid obstruction of the primary aperture by secondary optical elements, instrument packages, or sensors, and to provide ready access to instrument packages or sensors at the focus. The engineering… (Read More →)

1. In telephony, the condition that exists when an operational telephone instrument or other user instrument is in use, i.e., during dialing or communicating.
Note: Off-hook originally referred to the condition that prevailed when the separate earpiece, i.e., receiver, was removed from its switchhook, which extended from a vertical post that also supported the microphone, and which connected the instrument… (Read More →)

Synonym hotline.

In telephony, of a circuit, a signal indicating seizure, request for service, or a busy condition.

1. Pertaining to the operation of a functional unit when not under the direct control of the system with which it is associated.
Note 1: Off-line units are not available for immediate use on demand by the system.
Note 2: Off-line units may be independently operated.
2. Pertaining to equipment that is disconnected from a system, is not in operation,… (Read More →)

A particular form of authentication information binding an entity to a cryptographic key, certified by a trusted authority, which may be used for authentication without directly interacting with the authority [10181-2].

[A] cryptosystem in which encryption and decryption are performed independently of the transmission and reception functions. [INFOSEC-99]

The process of recovering nonprotected message traffic by use of an off-line processor or central processing unit.

Storage that is not under the control of a processing unit.

The process by which telephone calls that originate or pass through private switching systems in transmission networks are extended to stations in a public switched telephone system.