The scroll wheel is a mechanical device that is typically built into the mouse. It is used to move up and down web pages and other documents. The mouse wheel is a circular input device that can be found on the side of most mice.
The mouse wheel has the same functionality as the scroll wheel but it does not require as much effort to use. A person can scroll through a document by pressing the scroll button on their mouse, whereas they need to push their finger all the way down on a ball for each page they want to see with a scroll wheel.