An octagon is a polygon with eight sides and eight angles. The term "octagon" is derived from the Greek word "oktagōnos," which means "eight angles." The most familiar example of an octagon is the stop sign, which has a distinct octagonal shape. Regular octagons have equal-length sides and angles, with each internal angle measuring 135 degrees, while irregular octagons can vary in side length and angles. Octagons are often used in architecture, design, and geometric studies due to their symmetrical properties and balance.