A teleprinter (also called a teletype, teletypewriter and TTY) is a typewriter that sends a typed message to another place. A teleprinter has a typewriter keyboard, a local printer (so the user can see what has been typed) and a transmitter. Messages can be sent over wires or radio waves.
Teletypes were used mostly in the early to mid twentieth century. They replaced telegraphs, some of which also used keyboards, though not typewriter keyboards. Though teleprinters have been replaced by other technologies, TDDs (Telecommunications Devices for the Deaf), which are based on the idea and design of teletypes, are still used these days.