A regular polygon is one which has all its edges the same length, and all its vertex angles the same size. An n-sided polygon in which the sides are all the same length and are symmetrically placed about a common center (i.e., the polygon is both equiangular and equilateral). The sum of perpendiculars from any point to the sides of a regular polygon of n sides is n times the apothem.

There are two particular circles associated with any regular polygon. First is the circumcircle (R-radius) which is the circle drawn around the outside of the polygon so as to touch all its vertices (or corners). Second is the incircle (r-radius) which is the circle drawn around the inside of the polygon so as to touch all its edges.

The terms equilateral triangle and square refer to the regular 3- and 4-polygons, respectively. The words for polygons with sides (e.g., pentagon, hexagon, heptagon, etc.) can refer to either regular or non-regular polygons, although the terms generally refer to regular polygons in the absence of specific wording.

The names of polygons with a large number of sides are difficult to remember. For example; 28- and 46-sided polygons are called Icosikaioctagons and Tetracontakaihexagons respectively. However, many people use the form n-gon, as in 28-gon, or 46-gon instead of these names.