Rollovers are Web effects that alter the usual appearance of the Web page without switching the user to a different Web page. The primary example is the namesake behavior: When a user rolls the mouse so that the pointer passes over a defined area of a Web page, that same area of the page changes appearance in some way. Usually, this is done as a visual cue, emphasizing that the area is a hotspot that the user can click to make something happen, such as open another Web page.
There are other kinds of rollovers. Some rollovers are tied to other types of user actions, such as clicking or holding down the mouse button. Some rollovers triggered by a user action in one area of the Web page can cause another part of the Web page to change.