The number of sides a regular polygon has is indicated by the name of the polygon. For example, a pentagon has five sides, and an octagon has eight sides. The fewest number of sides a polygon can have is three, but there is no upper limit.
The name "polygon" comes from the Greek words "polus," meaning "many," and "gonia," meaning "corner" or "angle." To be classified as a regular polygon, all of the sides and angles must be congruent. A three-sided regular polygon is called an equilateral triangle. A four-sided regular polygon is called a square. The names of many-sided polygons can be constructed from Greek-derived number names, such as dodecagon for a 12-sided polygon or hexadecagon for a 17-sided polygon. However, past a certain number of sides, mathematicians normally use the abbreviation "n-gon," so a 25-sided polygon is called a 25-gon.