Definitions In an undirected graph,the degree of a vertex is the number of edges connected to this vertex. In an directed graph,the outdegree of a vertex is the number of edges that start from this vertex,and the indegree is the number of edges that end at this vertex. ■ Examples of graphs:airport system,traffic flow, friendship.Definitions ◼ In an undirected graph, the degree of a vertex is the number of edges connected to this vertex. ◼ In an directed graph, the outdegree of a vertex is the number of edges that start from this vertex, and the indegree is the number of edges that end at this vertex. ◼ Examples of graphs: airport system, traffic flow, friendship