So what exactly do UI and GUI stand for, and what's the difference? UI stands for user interface, and GUI (pronounced "gooey") stands for graphical user interface. To interface means to interact with, so the user interface is the set of devices that let the player interact with the game. The mouse, keyboard, game controller, touch screen, and so on are all part of the user interface. Graphical user interface is the subset of the user interface that is represented by graphics. So, onscreen buttons, drop-down menus, and icons are all part of a game's GUI.
This book will focus primarily on GUI design, but it will discuss some non-graphical aspects of user interface controls, like accessing data from the mouse, screen tap, keyboard, ...
