ball

a small ball that is set in a holder and can be rotated by hand to move a cursor on a computer screen.Similar to that of a traditional computer mouse, the trackball mouse is an input device and functions in the same way, except that the trackball mouse remains stationery and does not move about on the operating surface. The trackball mouse configuration has a small solid ball and typically two buttons placed strategically to allow effective pointing ability without the need of excessive arm and wrist movement. When using the trackball, the design encourages a natural position for the hand. The two buttons are located where the user would rest his fingers.Similar to that of a traditional computer mouse, the trackball mouse is an input device and functions in the same way, except that the trackball mouse remains stationery and does not move about on the operating surface. The trackball mouse configuration has a small solid ball and typically two buttons placed strategically to allow effective pointing ability without the need of excessive arm and wrist movement. When using the trackball, the design encourages a natural position for the hand. The two buttons are located where the user would rest his fingers.
A computer mouse is a hand-held pointing device that detects two-dimensional motion relative to a surface. ... Mice often also feature other elements, such as touch surfaces and "wheels", which enable additional control and dimensional input.
A computer mouse is an input device that is most often used with a personal computer. Moving a mouse along a flat surface can move the on-screen cursor to different items on the screen. Items can be moved or selected by pressing the mouse buttons (called clicking).