Source : Free On-Line Dictionary of Computing

local echo
     
         (Obsolete: "{half-duplex}") A mode of
        operation of a communications program or device in which it
        displays the characters the user enters at the same time as it
        sends them to the remote system.
     
        In communications between computers or computing processes,
        particularly those involving human keyboarding and/or reading,
        duplex came to mean the re-transmission of a keyboard
        character to the output display.
     
        Early input device such as the Teletype {ASR-33}
        {teleprinter}, being descended from the electric typewriter,
        printed all input characters as they were typed (i.e. they did
        local echo).  Local echo was typically optional on the {video
        terminals} that replaced them, and usually disabled in favour
        of {remote echo}.  A disadvantage of local echo is that it
        will continue, even when the communication circuit has failed,
        which can be misleading.
     
        (2000-03-30)