In matroid theory, a discipline within mathematics, a graphic matroid (also called a cycle matroid or polygon matroid) is a matroid whose independent sets are the forests in a given undirected graph. The dual matroids of graphic matroids are called co-graphic matroids or bond matroids. A matroid that is both graphic and co-graphic is called a planar matroid; these are exactly the graphic matroids formed from planar graphs.