These events correspond to user actions as the mouse is moved over various elements on the screen or as the user clicks the mouse buttons.
Note that some of these events are triggered in multiples as a result of a single action.
For example, as a mouse button is pressed, a mouse-down even is fired. As it is released, a mouse-up and a click event are fired. A click event is only fired once for each mouse-down and mouse-up pair.
A double-click requires two down-up cycles within quick succession but the mouse-down and mouse-up events will also fire.
The DOM standard refines the event model and creates a specific object class to handle Mouse Events. The event model will evolve as more browsers take on the DOM specified model.