other name: end, endvertex
    
    graph theory:
    If in graph G = (V, E) edge e=uv (where e`in`E and u, v`in`V), vertices u and v are called endpoints (or ends, endvertices).
    
    If uPv is path in graph G, u and v are called endpoints (ends) of path P. All vertices between u and v in path P are called inner vertices.
    
    It can be used for walk too.
    
    topology:
    Let `(:v_0,..., v_k:)` be a simplex. `(:v_0:)` and `(:v_k:)` are called endpoints.