1 The reflection of transmitted data back to its source (or, as a verb, to reflect transmitted data back to its source). For example, characters typed on the keyboard of a data terminal (connected to a computer) will not appear on the display of the terminal unless they are echoed. The echoing process may be done locally by the terminal itself, by a modem, by an intervening communication processor, or by the computer to which the terminal is attached.
2 A phenomenon in voice circuits (e.g. telephone circuits) that upsets the operation of modems. Most modems therefore incorporate echo suppression.