My Free GUI's
Abbreviated from Graphic User Interface, Is described as an imagery which allows the user to perform interactions within a software application, the kind that does a particular function without the need for a text based command, or imagery to suggest you are at a place where functions can be changed.
An example of this could be a symbol on your 'Ipad' camera function, by clicking the red button will take the picture and store it in the file folder, unless you click the delete symbol.
Menu and Inventory screens in games would be considered a 'GUI', as the user would use that type of interactive options to start/save there games or equip their player with a special item.
There are some user interfaces in games that players would use but not necessarily interact with. Mini Maps are a kind of GUI but are mostly considered a 'HUD', Heads Up Display.