The most common type of shape you'll encounter in geometry is the polygon. A polygon is any closed 2D shape that is convex and has straight edges. These shapes are useful for calculating area, perimeter, and a whole host of other calculations. Along with this, classifying polygons, including the many types of regular polygons and quadrilaterals, can help you recognize the many patterns hidden within these shapes. Fiveable's free geometry guides are here to teach you how polygons can be used to solve geometrical problems!