Windows, Microsoft, and third-party software makers supply numerous useful tools for the command line — but these are not always easy to use. Graphical user interfaces (GUI), on the other hand, ...
Graphical user interface is sometimes shortened to GUI. The user chooses an option usually by pointing a mouse at an icon representing that option.
Graphical User Interface is sometimes shortened to GUI (pronounced "gooey"). The user chooses an option – usually by pointing a mouse at an icon representing that option, then clicking to select.