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Communication, often two-way, of spoken information, by means of electrical signals carried by wires or radio waves. The term was used to indicate transmission of the voice, as opposed to telegraphy (done in Morse code and usually called "continuous wave" or CW transmission), radio teletypewriter (RTTY) transmission (also called FSK for "Frequency Shift Keying", the modulation scheme used by such machines), and later, facimile.
instrument designed for simultaneous two-way voice communication and the technological system through which it is employed. It is a central part of modern telecommunication.