The number of nodes in a graph is called its order.
Graph Order
See also
GraphExplore with Wolfram|Alpha
References
Skiena, S. Implementing Discrete Mathematics: Combinatorics and Graph Theory with Mathematica. Reading, MA: Addison-Wesley, p. 82, 1990.Referenced on Wolfram|Alpha
Graph OrderCite this as:
Weisstein, Eric W. "Graph Order." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/GraphOrder.html