Alternatively referred to as the Microsoft mouse, wheel mouse or scroll mouse, the IntelliMouse is an optical mouse brand first developed by Microsoft in 1996. It has a wheel between the left and right buttons that enable the user to scroll up and down a web page; as opposed to using the vertical scroll bar. The picture below shows an example of the original Microsoft IntelliMouse.
Due to the wide popularity of this mouse, it has become the standard mouse model used with most computers. Although "IntelliMouse" is a Microsoft trademark, wheel mice are developed by every mouse manufacturer today.
Also see: Mouse terms