If the graph of a graph G can be drawn on a plane so that the edges of the graph do not intersect except the vertices, it is said that the graph G can be embedded in the plane;

A graph that can be embedded in a plane is called a planable graph.

2. Non-planar diagram: a diagram that cannot be embedded in a plane under any circumstances;

3. Plan: embedded in the plan;

4. Maximum floor plan:

If G is a simple planable graph and any two nonadjacent vertices of G are attached with an edge, it becomes a nonplanable graph.

5. Minimum non-planar plan:

If G is a nonplanar graph, but any edge in G is deleted, then G becomes a planable graph.