An instance is nothing more than a copy of a library symbol that has been placed on the stage. When a symbol has been changed, all instances of that symbol will change accordingly. Also, because you are using an instance of the symbol, that again is no more than just a copy of the original, you can adjust certain settings of that instance, such as size, coloring, and alpha, without altering other instances of the symbol or the symbol itself. When we get into ActionScript later in this chapter, you will see the importance of instances because they will have unique names, and that is how to control them with ActionScript.
Remember that symbols are items held in the library and instances are copies of symbols that have been placed on the stage.