Multigraph Definition

(mathematics, graph theory) A set V (whose elements are called vertices or nodes), taken together with a multiset E, each of whose elements (called an edge or line) is a cardinality-two multisubset of V.

(mathematics, graph theory, less commonly) A set V (as before), taken together with a multiset E, each of whose elements is a cardinality-two subset of V.

Multidigraph.