The next Hawaii Flash User Group meeting will be on OOP in Flash.
What is OOP?
OOP stands for Object-Oriented Programming. When you are coding big projects you will have hundreds (even thousands) of lines of code and it can get very unorganized. This is where OOP comes in. You can make classes, which are external .as files (ActionScript files) and import them into your project. You can then use the methods and properties in that class.
Also, instead of having to write the same code over and over again you could make a class containing that code. Then whenever that code is needed instead of having to write it all you can just call it from the class.