Ans: Dynamic keyword-> Specifies that instances of a class may possess dynamic properties added at run time.
For example: In Java, if you?ve created an object from a particular class, you can use only properties and methods that were defined in this class. For example, if the following class:

class Product{
String name;
}

you can only manipulate with the name property:

Product p = new Product();
p.name = ?colddrink?;
System.out.println(p.name);

ActionScript dynamic classes, which allow you to programmatically add new properties and behavior to classes during the run-time. Just add the magic keyword dynamic to the class definition:

dynamic class Product{
var name:String;
}

Now let?s add dynamically two variables name and price and the function printme() to the object of type Person:

Person p= new Person();
p.name=?colddrink?;
p.price=12;
p.printMe = function () {
trace (p.name, p.price);
}
p.printMe(); // colddrink 12