Scroll wheel

A scroll wheel is a wheel used for scrolling on an electronic visual display. The term usually refers to a wheel found on a computer mouse, in which case it is also called a mouse wheel. It is often made of hard plastic with a rubbery surface, centred around an internal rotary encoder. It is usually located between the left and right mouse buttons and is positioned perpendicular to the mouse surface. Sometimes the wheel can be pressed to provide additional input, in effect functioning as an additional mouse button.