Graph
A graph G = (V, E) contains a (finite) set that is denote by V, or by V(G) if one wishes to make clear which graph is under consideration, and a collection E, or E(G), of unordered pairs {u, v} of distinct elements from V. Every element of V is called a vertex or a point or a node, and each element of E is known as an edge or a line or a link.
Basically, a graph G is an ordered pair of disjoint sets (V, E), where E ⊂V × V. Set V is called the vertex or node set, in which set E is the edge set of graph G. Typically, it is assumed that self-loops (that is edges of the form (u, u), for some u ∈ V) are not contained in a graph.