What is a directed graph?

A directed graph (digraph) is a graph in which every edge has a direction.

Formally: A directed graph is a set of vertices V and a set of ordered pairs of vertices E, that is, G = (V, E), where each edge is (u, v), not just {u, v}.

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#Main idea

An edge (u → v) means a connection only from u to v, not the other way around.

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#Example

If there are vertices A, B, C, and edges:

• A → B,
• B → C, then you can get from A to C, but not the other way around, if there are no reverse edges.

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#Typical applications

• Follows on social networks (A follows B ≠ B follows A).
• Data or process flows.
• Dependencies between tasks (for example, a dependency graph during compilation).

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Summary: in a directed graph, edges lead in a specific direction, which makes connections one-way.