A graph's circuit rank is the minimum number of edges that have to be removed for the graph to become a tree or forest. Is there a term that represents the minimum number of *vertices* that we must remove to get a tree or forest? I am working on a project that involves reducing cyclic graphs to trees by removing vertices, but I can't seem to find a term that refers to the quantity above. Vertex connectivity is the closest I've found, but it is still a different concept. Thanks in advance.