Graph: Directed vs Undirected

There are different kinds of graphs! Two broad category 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. The directed edge shows a one-way traffic from stop $A$ to stop $B$.

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