Definitions

First, some definitions:

Application: A program you use as a tool such as a terminal emulator, clock, a calendar program, a text editor, etc.
Cursor: A small box (or underline) on the screen that shows where the characters will go when you start typing.
Display: The screen of your workstation.
Icon: A small picture that represents an application that is not in use. To iconify an application is to close that application's window and make its icon appear at the edge of your screen. To deiconify an application is to click on its icon and open it up again.
Mouse: A thing with buttons on it that allows you to point at objects on the screen. The mice we get with Sun workstations have 3 buttons.
Mouse Cursor: The small object on the screen that moves when you move the mouse. The mouse cursor has different shapes depending on what you are doing with it.
Root Window: The area of your screen that doesn't have a window over it: the "background".
Terminal Emulator: An application that just mimics a computer terminal: sending characters to a computer and displaying what the computer sends back. Also known as "xterm", it's possible to have more than one xterm window on your screen with each one "talking" to a different computer.
Window: An area on your screen that has an application going on inside.
X Server: The program that draws things on the screen of your workstation.