Outerplanar graph --- внешнепланарный граф.
A graph is outerplanar if there is a crossing-free embedding of in the plane such that all vertices are on the same face. is outerplanar iff contains no subgraph homeomorphic to or by a homeomorphism that deletes degree-2 vertices but does not add them.
is -outerplanar if for is an outerplanar graph and for has a planar embedding such that if all vertices on the exterior face are deleted, the connected components of the remaining graph are all -outerplanar. See also Halin graph.