Graphical User Interface (GUI): It stands for "Graphical User Interface," and is pronounced as ‘gooey.’ It refers to the graphical interface of a computer which permits users to click and drag objects with a mouse rather than entering text at a command line. Two of the most admired operating systems, Windows and the Mac OS, are GUI-based. The graphical user interface was primary introduced to the public by Apple with Macintosh in the year 1984. Though, the idea was really taken from a previous user interface developed by Xerox.