Planar graph --- планарный граф, плоский граф.
A crossing-free embedding of a graph in the plane is given by drawing a graph in the plane with points representing vertices and curves representing edges such that no two curves for edges intersect except at common endvertices. is a planar graph if there is a crossing-free embedding of in the plane.
In other words, a graph (digraph) is called a planar graph, if there is a projection of the vertices and edges of into the plane such that the intersections of the projections of edges occur at the projections of vertices, and is a Jordan-curve from to . The projection is called a planar embedding of . It divides the plane into a number of connected regions, called faces, each bounded by the projection of edges of the graph. There is always a face with an infinite area, which is called the exterior face.
- Plane graph.