TTY (Text Telephone) is a device that allows individuals who are deaf, hard of hearing, or have speech disabilities to communicate over the telephone using text. Users type their messages on a keyboard, and the text is transmitted over the phone line to another TTY device, where it is displayed on a screen. This technology enables real-time conversation without the need for voice. TTY devices often include features like a built-in printer for hard copies of conversations and a visual display for easy reading. They are commonly used in conjunction with relay services, where an operator facilitates communication between TTY users and those using standard telephones.