Is a telephone service, available in analogue, digital phone systems and Voice over Internet Protocol (VoIP) applications, that transmits a caller's number to the called party's telephone equipment during the ringing signal, or when the call is being set up but before the call is answered. Where available, caller ID can also provide a name associated with the calling telephone number. The information made available to the called party may be displayed on a telephone's display or on a separately attached device.

CID = Caller ID (Caller identification)

CNID = Calling Number Identification

CLID = Calling Line Identification

CLIP = Calling Line Identification Presentation