Beginner's Guide to Adobe Flash/Symbols/Button
A Button Symbol is different from the other two symbols because it has a unique timeline. Used for creating interactive buttons, they have a timeline limited to four frames, which are referred to as states. The four states are labelled “Up” - (when the mouse cursor is not over the button), “Over” - (when the mouse cursor is over the button, but the mouse button is not pressed), “Down” - (when the user presses the mouse button over the button itself), and “Hit” - (this is a nonvisual state that enables you to define the area that will activate the button’s other states). Each state can be defined with graphics, symbols, and sounds. Button Symbols however, can be redundant, as it's possible by using ActionScript to produce a button using a MovieClip.