Telecommunications relay service

A telecommunications relay service (TRS; also a relay service, IP-relay, or web-based relay service) is an operator service that allows people who are deaf, hard of hearing, deafblind, or have a speech disorder to place calls to standard telephone users via a keyboard or assistive device. Originally, relay services were designed to be connected through a TDD, teletypewriter (TTY) or other assistive telephone device.

Source: Wikipedia — Telecommunications relay service (CC BY-SA 4.0)