The scene graph is the ordered collection of nodes that make up the 3-D world. The scene graph consists of at least one node. The scene graph is more than just a collection of nodes, however. It defines the order of the nodes contained within it. The node represents the geometry, properties, and grouping of the objects in the 3-D world.
This order of the nodes is important. A node can affect each and every node that comes afterward in the scene graph. There are ways to prevent this interaction and these methods are discussed in these web pages.