trackball definition by Webster's New World
trackball definition by American Heritage Dictionary
trackball - Computer Definition
A stationary pointing device that contains a movable ball rotated with the fingers or palm. From one to four keys are located in various positions depending on the unit. In the late 1980s and 1990s, Kensington Microware popularized the trackball with its Turbo Mouse for the Macintosh. Turbo Mouse for Windows was subsequently released, and over the years, the Turbo Mouse evolved into the Expert Mouse and Orbit brands. The advantage of the trackball, and the reason many people like it, is that the unit remains in the same position on the desk, and only the ball is moved. See mouse, pointing stick and touchpad.