Wiktionary
scroll wheel
n. (context computing English) A hard plastic or rubbery disc on a computer mouse, used for scrolling.
Wikipedia
Scroll wheel
A scroll wheel (or mouse wheel) is a hard plastic or rubbery disc (the " wheel") on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons.
Usage examples of "scroll wheel".
Twirling the scroll wheel on his mouse took him farther down the same page, to a study by researchers named Heim and Hursch that showed that over 50 percent of castrated rapists “.