Definition:Null Graph

The null graph is the graph which has no vertices.

That is, the null graph is the graph of order zero.

Beware confusion with the concept of an edgeless graph which, although it has vertices, it has no edges.

The null graph also has no edges, so can also be referred to as an edgeless graph.

It is called the null graph because, from Empty Set Unique, there is only one such entity.

Beware
Some treatments of this subject do not recognise the null graph as a graph at all, requiring that the vertex set of a graph can not be empty.

Hence the term null graph is frequently seen to mean what this site calls an edgeless graph.