CUI is either "Character User Interface", "Console User Interface", or "Captive User Interface". The first two are mostly orthogonal to "Command Line Interface" (CLI), which can be character based or graphical. The last asserts that the interface fails to play well with the shell, which is nearly always true of GUIs and is frequently true of console programs that make heavy use of ncurses (though not always, and can be true without that).