Booting is starting a computer's operating system, so rebooting is to start it for a second or third time.
Rebooting is usually necessary after a computer crashes, meaning it stops working because of a malfunction. Rebooting allows the computer to restart and get back to working normally.
GUI stands for Graphical User Interface while CUI stands for Character User Interface
What is the difference between GUI and CUI?
GUI
A graphics-based operating system interface that uses icons, menus and a mouse (to click on the icon or pull down the menus) to manage interaction with the system.
CUI
A conversational user interface (CUI) is a user interface for computers that emulates a conversation with a real human.