Caller ID - Wikipedia, the free encyclopedia

Caller ID (caller identification or CID, and more properly calling number identification - CNID) is a telephony service that transmits the caller's telephone 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 is visible on a small liquid crystal display imbedded on the telephone, or on a separate unit which is connected to the telephone.
Caller ID is often helpful for tracing down prank calls and telemarketers. The concept behind caller ID is the value of informed consent; however, it also poses problems for personal privacy.

Caller ID - Wikipedia, the free encyclopedia