Is it farther or further?
(Obsolete: "full-duplex") A mode of operation of communicating programs or devices in which the sending system does not display the characters the user enters, but only sends them to the remote system which then "echoes" them back to be displayed to the user. This lets the operator see not only typing errors, but also transmission errors. This is now the usual mode of most systems with remote users.
Contrast: local echo.