Adjective
outerplanar (not comparable)
(mathematics) Describing a graph having a planar embedding such that the vertices lie on a circle and the edges lie inside that circle
In analogy to the characterizations of the outerplanar and planar graphs as being the graphs with Colin de Verdière graph invariant at most two or three, the linklessly embeddable graphs are the graphs that have Colin de Verdière invariant at most four. Source: Internet
Every outerplanar graph is planar, but the converse is not true: K 4 is planar but not outerplanar. Source: Internet