call forwarding; call diversion
A telephone service that redirects incoming calls to another number. Common in business and personal phone settings.
If you set up call forwarding, you can receive calls to the office even when you're out.
転送 is the general act of forwarding or transferring something, while 転送電話 specifically refers to the telephone call forwarding service.
Compound of 転送 (forwarding) and 電話 (telephone).