The defining characteristic of the decathlon is its format, consisting of ten different athletic events held over two days. These events test a wide range of skills, including speed, strength, agility, and endurance. Participants earn points based on their performance in each event, with the athlete accumulating the most total points declared the winner. The decathlon is often seen as a true test of an athlete's overall versatility and athleticism, making it a popular event in track and field competitions.