A pointing device consisting of a ball sitting in a socket that contains sensors to detect the rotation of the ball about its two axes. It looks like an upside-down mouse. To move a cursor, the user rolls the ball with his or her thumb or palm. Trackballs are common on CADworkstations, for ease of use, and on laptops, for use where there isn't enough surface area for a mouse. Some trackballs clip onto the side of a keyboard.