In Computer Graphics a mesh is a surface, usually piece-wise linear, describing the object to be rendered.
It's quite common, for instance, to describe a three-dimensional object as a set of vertices, and then defining the neighbourhood relations between them: in this way you get a mesh.

Another piece of information: at the last SIGGRAPH, a whole session was devoted to subdivision, an algorithm to iteratively refine a mesh, increasing the number of polygons belonging to the surface.