A series of vertices that define a plane in 3D space. Most RT3D engines use polygons to make the surfaces of their objects. A polygon can be made up of 1 or more triangles, like a quad is made of two triangles, a pentagon is made of three triangles, etc. Some engines support multiple polygon types, but triangles are the most common. Some people use the term polygon to specify a quad, others use it when talking about triangles. Polygons are also called polys, or sometimes n-gons. See also faces, fans, quads, strips.