Action Message Format (AMF) is a protocol that is used to serialize the data coming into Flash Player or going out to other programming environments that need to communicate with Flash Player. Say, if you create in Java an instance of the class MyOrder, this instance can be converted into a string of bytes, sent over the wire to Flash Player and then recreated there as an instance of the ActionScript object. The rules of how to do this are defined by a communication protocol, such as AMF.