Directed vs Undirected Graphs
In an undirected graph, an edge represents a bidirectional relationship, so an edge between A and B allows traversal in both directions. In a directed graph, an edge has a source and destination, so A to B does not imply B to A.
Undirected edges have no direction.
Directed edges have source and destination.
Undirected degree counts incident edges.
Directed graphs use indegree and outdegree.
Social connections can be modeled as undirected; dependencies commonly use directed graphs.