As Damiano Jack Lee mentions, the related quantity $|E|-|V|+1$ (your number plus 1) |V|-|E|$is often called the Euler characteristic of the graph. I have also heard$|E|-|V|+1$called the cyclomatic number. 1 As Damiano mentions,$|E|-|V|+1$(your number plus 1) is often called the Euler characteristic of the graph. I have also heard$|E|-|V|+1\$ called the cyclomatic number.