A polygon with five sides is called a pentagon. In Greek, "pente" means "five." When math textbooks discuss pentagons, they are typically referring to a polygon with five equal sides, otherwise known as a regular pentagon.
The sum of all the angles inside of any polygon drawn on a flat surface is 540 degrees. In a regular pentagon, each angle has 108 degrees. In other pentagons, an individual angle cannot be more than 540 degrees or less than 0 degrees. All regular pentagons have an area that can be calculated by multiplying the square of the length of an individual side by the constant 1.72.
If a pentagon consists of equal sides and equal angles, it is referred to as a regular pentagon; otherwise, it is called an irregular pentagon. A pentagon consists of five straight, connected sides. If one of the five sides of a given shape is a curved line or if the five-sided shape is not a closed figure, then it is not a pentagon.