A decagon is a polygon that has ten sides and ten angles. The term comes from the Greek words "deka," meaning ten, and "gonia," meaning angle. Decagons can be regular, where all sides and angles are equal, or irregular, where they differ in length and angle size. In geometry, the sum of the interior angles of a decagon is 1,440 degrees. This is calculated using the formula (n-2) × 180, where n is the number of sides. Decagons can be found in various designs, including architecture and art, showcasing their unique shape.