Techopedia explains
Graphical User Interface (GUI)
In the late 1970s, the Xerox Palo Alto research laboratory created GUIs, which are now common in Windows, Mac OS, and many software applications. By using specially designed and labeled images, pictures, shapes and color combinations, objects were depicted on the computer screen that either resembled the operation to be performed or were intuitively recognized by the user. Today, each OS has its own GUI. Software applications use these and add additional GUIs of their own.
How we interface with a computer is constantly being revised and reinvented. Human ingenuity has brought users from the keyboard to the mouse and trackball, touch screens and voice commands.
A visual language has evolved as GUI has become commonplace in both operating systems and software applications. Even those with few computer skills can now, through the use of GUI, learn how to use computer applications for word processing, finances, inventory, design, artwork or hobbies.