Tessellation is the process through which forms fit together in a pattern without gaps or overlaps. The word comes from Latin tessera, which means "little cube." When used in reference to graphics hardware and software, it has a more specific meaning: the process of dividing each triangle in a polygon into many small triangles, typically four per vertex but any number may be used. Because polygons are made up of many sides, they can be thought of as being composed of many triangles. In fact, there are only a few types of shapes in nature that cannot be represented as some type of polygon (circles and spheres). Polygons can also be described as closed surfaces; that is, surfaces with one point identified as the beginning and another as the end. Closed planes are examples of polygons, as are rings (such as a rope) and cones (such as candle flames). A polyhedron is any solid whose every surface is divided by itself or some other surface into several convex pieces. All cubes, pyramids, and tetrahedrons are examples of polyhedrons. A mesh is a structure used in finite element analysis to divide a computational domain into smaller elements for modeling purposes.