A trackball is an input device, similar to a mouse, that uses a ball to control a cursor on a computer screen. The user rolls the ball with their fingers or thumb, and the movement of the ball is translated into cursor movement on the screen.

Trackballs were very popular in the early days of personal computers but have become less common since the rise of the mouse. They are still used in some specialized applications, such as CAD/CAM design and gaming, because they offer several advantages over mice, such as:

* Ergonomics: Trackballs are more comfortable for some users because they don't require the user to move their entire hand.

* Precision: Trackballs can be more precise than mice, especially for tasks that require fine control.

* Space saving: Trackballs take up less desk space than mice.

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