Sentence:  If "n" is finite, the <WSD>regular map</WSD> is a tessellation of the plane by congruent "n"-sided polygons, "m" of which meet at each vertex. 
Meaning of the word marked with <WSD> tags:  A symmetric tessellation of a closed surface; a decomposition of a two-dimensional manifold into topological disks such that every flag (incident vertex-edge-face triple) can be transformed into any other flag by a symmetry (i.e., an automorphism) of the decomposition.