A mouse is a pointing device and functions by detecting two-dimensional motion relative to the underlying surface. It usually consists of a small plastic case with one or more buttons. Some mice (mouses) also have "wheels", for performing various system-dependent operations. The mouse's motion results into the motion of a pointer on monitor screen.
A mechanical mouse has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
An optical mouse uses a light-emitting diode and photodiodes to detect movement relative to the underlying surface, rather than moving some of its parts as in a mechanical mouse. Optical mice have no rolling parts, and therefore (unlike mechanical mice, which clog up with lint) they do not normally require maintenance other than removing debris that might collect under the light-emitter.
A cordless or wireless mouse is not physically connected to the CPU. Instead it relies on infrared or radio waves to communicate with the computer. Cordless mice are more expensive than both serial and optical mice.
The two-button mouse with scrolling roller wheel has become the most commonly available design. The primary mouse button is located on the left-hand side of the mouse by default, for the benefit of right-handed users. The left-handed users can reverse this configuration via software. The second (right by default) button is used to invoke a contextual menu in the computer's software user interface, which contains various options relating to the program/icon/link on which the button has been clicked.
Mice, like keyboards, also come in different connection type variants viz. AT, PS2, USB and wireless.