In the mathematical field of graph theory, an instance of the Steiner tree problem (consisting of an undirected graph G and a set R of terminal vertices that must be connected to each other) is said to be quasi-bipartite if the non-terminal vertices in G form an independent set, i.e.
A particular case of the Steiner tree problem (concerning an undirected graph G and a set R of terminal points that must be connected) is called quasi-bipartite if the non-terminal vertices in G form a separate group, meaning no two non-terminals are directly linked.