RJ11 is used for the purpose of connecting telephone systems. The RJ11 is the most common type of registered sockets today and it is used for the purpose of terminating phone lines
Telephone Line Jack Unit- RJ11 Socket
A registered jack (RJ) is a standardized telecommunication network interface for connecting telephone systems. The RJ11 is suitable for both home and office installations. It is normally used for analogue voice line connections.