Ans:

MovieClip:

The MovieClip class inherits from the following classes: Sprite, DisplayObjectContainer, InteractiveObject, DisplayObject, and EventDispatcher. Unlike the Sprite object, a MovieClip object has a timeline. Flash uses the metaphor of a timeline to convey animation or a change in state. Any visual element that employs a timeline must be either a MovieClip object or extend from the MovieClip class. While ActionScript can direct any movie clip to stop, play, or go to another point on the timeline, it cannot be used to dynamically create a timeline or add content at specific frames; this is only possible using the Flash authoring tool.

for example:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application 
xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute" width="646" height="319">

  <mx:Image id="img" x="10" y="41" width="290" 
  height="267" source="rotating.swf"/>
  <mx:Image id="imgDup" x="346" y="41" width="290" height="267"/>
</mx:Application>

In this example you can see how we can load the swf file as a movie clip.