Definition:Null Graph

Definition
The null graph is the graph which has no vertices.

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

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 be non-empty.

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