Graph: Directed vs. Undirected

There are different kinds of graphs! Two broad categories are directed vs. undirected graphs.

The difference is in the type of edge they have.

For example, $A$ and $B$ may represent two bus stops. Therefore, the directed edge shows one-way traffic from stop $A$ to stop $B$.

On the other hand, $A$ and $B$ may represent two individuals on Facebook. The undirected edge represents the friendship between them.