A trackball, sometimes trackerball, is a computer pointing device similar to a mouse where the ball is placed on the top and manipulated manually. When mice switched to solid state optical sensors, trackballs did the same, but the ball remained present and the optical sensor observes the ball's surface instead.
External trackballs are desktop input devices that sit beside the keyboard. These are still widely available today.
Trackballs were widely used in integrated fashion. Apple's first laptop range, the Apple PowerBook 100 series, were notable for having an integrated trackball in front of the keyboard. In comparison, Toshiba laptops required a separately-carried trackball that attached to the side of the machine. Trackballs provide far superior cursor manipulation compared to a trackpad, but the combination of moving parts and bulk led them to fall out of favour compared to trackpads, similar to how laptops universally use scissor switch keyboards to keep the size and weight down.
The IBM Trackball Keyboard series was among several companies' product ranges that contained a trackball integrated into a standalone keyboard. Cherry have also produced G84-series keyboards with integrated trackballs.
Some BlackBerry models use miniature trackballs.
Qtronix KT-30M integrated trackball