Concept: undirected graph
An undirected graph G = (V, E) is connected if, for any vertices u, v ∈ V, there exists a path in G connecting u to v.
Concept: directed graph
A directed graph is said to be strongly connected if, for any vertices u, v ∈ {A, B, C, D, E}, there exists a directed path from u to v and also from v to u.