A surface with boundary is a topological space obtained by identifying edges and vertices of a set of triangles according to all the requirements of a surface except that certain edges may not be identified with another edge. These edges are called boundary edges and their vertices are called boundary vertices (Henle 1994, p. 129).
Examples of surfaces with boundary include the cylinder and Möbius strip (Henle 1994, pp. 110 and 129).
