A gadget is an application control symbolized by a graphic image that can
be operated with the mouse or keyboard.  The imagery used for a gadget
could look like a switch, a knob, a button, or just about anything.
Intuition supplies some pre-fabricated gadgets, called system gadgets, for
controlling window and screen arrangements.  Other gadget types allow the
user to select colors, enter text or numbers, and perform other simple
operations.

     Figure 2-3: An Intuition Window with Gadgets 

Most of the user's input for a typical Intuition application will be
obtained with gadgets.  Gadgets are discussed in detail in Chapter 5,
"Intuition Gadgets".  Additional information on programming gadgets for
Release 2 of the operating system can be found in Chapter 15,
"GadTools Library".