DefinitionTTY/TDD stands for Teletypewriter/Telecommunications Device for the Deaf. This involves a user terminal with keyboard input and printer or display output used by the hearing and speech impaired. The device contains a modem and is used over a standard analog phone line. If a recipient does not have a corresponding terminal device, TTY/TDD users dial a relay service composed of operators who receive the typed messages, call the recipients and speak the messages to them. The operators also type the responses back to the TTY/TDD user.
Terms and DefinitionsGenerated June 22, 2026
