CK-12 Foundation
Ck 12: Geometry: Polygons Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide focuses on polygons: convex vs concave, interior and exterior angles, and basic terminology for common polygons.
Math Is Fun
Math Is Fun: Regular 2 D Shapes
This tutorial provides illustrations for regular 2-D shapes as well as a definition for polygons and for regular polygons.