Graphical user interface (GUI) is a computing term for a user interface that allows interaction through a program with images instead of command line/text prompts.
GUIs are found on nearly all electronic devices and programs used on computers, media devices, smartphones, gaming handhelds, office equipment and other appliances.
Required actions are performed through use of the GUI rather than needing to type long lines of text/code.
For an example of GUI used in everday appliances is the copy machine in your office. Without a GUI that makes it easy to press how many copies you want, you would have to type in a text telling the machine what you want to do.