Ringer ID - definition
Every phone which allows users to save contacts in the device’s internal phonebook gives access to the user to a specific ringtone for a selected contact in the phonebook. This is used to rectify the other callers from specific numbers.
i.e.: Suppose, there are 5 ringtones in a phone named: Ring1, Ring2, Ring3, Ring4, Ring5. Among these 5 options, you chose Ring4 as the common ringtone for all the incoming calls. But you chose Ring2 only when your Mom/Dad is calling just to know it is from your home so that you don’t miss their important calls.
i.e.: Suppose, there are 5 ringtones in a phone named: Ring1, Ring2, Ring3, Ring4, Ring5. Among these 5 options, you chose Ring4 as the common ringtone for all the incoming calls. But you chose Ring2 only when your Mom/Dad is calling just to know it is from your home so that you don’t miss their important calls.