A graph is a forbidden subgraph if its presence as a subgraph of a given graph means it is not a member of some family of graphs. For example, a bipartite graph is a graph that does not contain an odd cycle as a subgraph. More generally, there may be a family of (minimal) subgraphs whose presence characterizes if a given graph has some property. For example, a graph on 9 or fewer vertices is a unit-distance graph iff it does not contain one of a set of 74 minimal graphs as a subgraph. The following table summarizes some graph families which have forbidden subgraph obstructions. family | obstruction bipartite graph | cycle graph C_n for n = 3, 5, ... unit-distance graph on <9 vertices | 74 minimal graphs

forbidden induced subgraph | forbidden minor | subgraph