Computer mouse is a device for manipulating figures on a computer screen without using a keyboard. It is an input mechanism that bears some resemblance to the animal. Computer operations often involve creating, selecting, or manipulating items on a screen. A computer mouse can perform these tasks by pointing or taking the cursor to the desired place, on the screen.
It is a hand operated pointing device that senses movements as it is dragged across a flat surface and conveys this information to the computer. In this way images, and text can be moved around on the screen, or a particular operation selected from a menu. A mouse usually has one or three buttons that are clicked when the user wants to register the cursors current position.
At present, there exist a number of different types of computer mouse but the most commonly used one is the 
mechanical mouse. It contains a ball on its underside that rolls on a surface as the mouse is moved. There are also two small wheels inside that touch the ball and spin as the ball rolls. These wheels are connected to devices that measure the distance moved. The non-mechanical mouse is also popularly known as optical mouse. Such a mouse does not contain a rolling ball or spinning wheels but slides over and scans with laser light a special pad ruled with alternating dark and light lines to form a grid.