Short for Graphical User Interface [L1 ]
Many toolkits for the creation of GUI's exist. In the Tcl world, Tk is one of the most commonly used, but there are Tcl bindings for other toolkits as well; see for instance Alternative GUI Toolkits.
AM Here is a link to a page that holds a lot of pointers; it is called the GUI Toolkit Framework Page, [L2 ]