Pronounced "gooey", GUI stands for Graphical User Interface.  It consists of graphic or visual elements such as windows, icons and buttons that allows a user to interact with a computer operating system.  GUI is distinguished from Command Line Interface (CLI), which is a purely text based way of submitting commands to a computer system.  The traditional method of engaging a GUI on a computer is via a mouse and keyboard, however touch based GUIs are very common now with the rise of tablets and smartphones, and can be found on many newer desktop and laptop computers as well.