Concept of DisplayList
DisplayObjects must be registered for the list of a DisplayObjectContainer (often called 'DisplayList') to show themselves in it with actionscript 3.
DisplayList
The addChild() and the addChildAt() method is used to add a instance of a displayObject to its own displayList. The addChild() handles the depths automatically.
public addChild(child:DisplayObject) : DisplayObject public removeChild(child:DisplayObject) : DisplayObject public addChildAt(child:DisplayObject, index:int) : DisplayObject public setChildIndex(child:DisplayObject, index:int) : Void
What's Sprite Object?
Movieclip class is a class extended from sprite class and there are no difference between them except movieclip class has a timeline and scenes.
var sprite:Sprite = new Sprite();