To give an example, a hexagon is a collection of 6 points in the plane. The order in which the points are taken is important. This ordering is cyclic, in that 1 comes before 2 and after 6.

An octagon is just like a hexagon, except that there are 8 points. In general, a N-gon is a collection of N points in the plane, ordered as above. The words N-gon and polygon are synonymous.