An edge is incident on a vertex if the vertex is one of the end points of the edge. Also, two edges are incident if both of them share a vertex. If we consider the following diagram, we can see the incident edges (e1, e2), (e2, e3), and (e1, e3) sharing vertex 1 among themselves. We also have incident edges (e3, e4) that share vertex 4 among themselves and edges (e2, e4) that share vertex 3 among themselves. Similarly, we can say that vertex 1 is incident on edges e1, e2, and e3, vertex 2 is incident on edge e1, vertex 3 is incident on edges e2, and e4, and vertex 4 is incident on edges e3, and e4: