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Definition: TDD/TTY


(Telecommunications Device for the Deaf/TeleTYpewriter) A type of "telecommunications relay service" (TRS) for the hearing or speech impaired. Introduced in 1964, a keyboard terminal with printer or screen output contains a modem for transmission over a standard analog phone line. If a recipient does not have a corresponding terminal, TDD/TTY 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 TDD/TTY user. See VRS.