Pronounced gooey. A visual computer environment that uses graphical images such as icons, menus, and dialog boxes to represent files, file folders, programs, and options to ease the interface between the user and the computer. The user can use a mouse, keypad, thumbpad, or other device to manipulate an icon, button, scroll bar, check box, or other graphical item to activate a routine to activate a program feature, such as opening or closing a file.The first GUI was invented by a research team at the Xerox Palo Alto Research Center (Xerox PARC). GUI has largely superseded the Command Line Interface (CLI) in computer and communications gear except for routers and switches.