A graph can be directed or undirected. With an undirected graph edges have no orientation, for example, a diplomatic relation between two nations may be mutual and thus have no direction to the edge between the nodes. These undirected graphs have unordered pairs of nodes, that means we can just switch them round, if Jane and Paul are married, we can say Jane is married to Paul or we can say Paul is married to Jane it makes no difference and thus it is an unordered pair. A directed graph is a set of nodes connected by edges, where the edges have a direction associated with them, that is typically denoted with arrows indicating the direction, for example, if we were drawing a graph of international trade the graph might have arrows to indicate the direction to the flow of goods and services.