Symbol

From Flash Wiki

A symbol is a reusable object used/created in Flash. A Symbol can be reused throughout your movie or imported and used in other movies. There are three types of symbols: Graphics, Buttons, and Movieclips.

[edit] Movieclips

Movieclip symbols are reusable pieces of flash animation - consisting of one or more graphic/button symbols - thus they are flash movies within your flash movie. They have their own non-restricted Timeline (any number of layers and frames - just like the main timeline) that plays independent of the main movie's Timeline. The best thing about using movieclips is that you can control them from actionscript - you can change their dimensions, position, color, alpha, and other properties and can even duplicate and delete them.

[edit] Buttons

Button symbols are used for timeline navigation - They add interactivity to the movie and respond to mouse clicks, key press or rollovers/rollout, and other actions. You define the graphics associated with various button states (Up/Over/Down/Hit), and then assign actions to the instance of a button. They have 4 frames in their timeline - one each for the up, over and down states, and one to define the hit area of the button.

[edit] Graphics

Graphic symbols are reusable static images that are used mainly to create animations. Any drawn vector/plain text/imported bitmap (photo), or combinations of these, can be converted into a single controllable object: as a graphic symbol.