Directed vs. Undirected Network:
In a directed network, connections between nodes are directional. For example, in a Twitter network, Smith might follow Jones but that does not mean that Jones follows Smith. Each directional relationship would have an edge to represent it, typically with an arrow. In an undirected network, relationships are non-directional by their nature. For example, in a Facebook network, if Smith is friends with Jones that means that Jones is friends with Smith.