Polygon is another word for face, face being for adjacent edges connected together.
We categorize polygons by how many sides they have, the ones with three sides we call triangles, or tries, seeing as they're triangle shaped.
The four sided ones we call quads, which are the ones that people like to tell you to use the most, and everything with more than four sides we call N-Gons, where N is a variable for the number of sides the face has. Everything N-Gon is BAD in general. Although there are always engines that can handle N-Gons most probably don't.
And if you ever get a modeling job and your boss gives you a assignment it's most likely that he'll tell you to use only quads or only tris.
Alucard94, the member of the future of the past.