interface: A small, flat rectangular pad that Apple developed to replace the trackballs in PowerBooks. It uses capacitance-sensing like the touch-sensitive buttons in elevators, and has 387 points-per-inch sensitivity. Like the mouse, it is a relative-motion device - when you raise your finger and put it back anywhere on the pad, the cursor stays put.
n. A pointing device consisting of a small, flat pad that is sensitive to touch. Users move the mouse cursor on screen by touching the trackpad and moving their fingers across the trackpad's surface. Such devices are most commonly installed on laptop computers. See also pointing device.