Caller ID (caller ientification, CID, or more properly calling number identification) is a telephone service, available on POTS lines, 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 made visible on a telephone's own display or on a separate attached device.