P90X is an extreme 90-day fitness program created by Tony Horton, combining cardio, strength training, yoga, and a nutrition plan to enhance fitness and avoid workout plateaus through 'muscle confusion.' Launched in 2004, the program has become Beachbody's best-selling product, contributing significantly to its revenue with millions of copies sold. The system includes a diverse range of workouts and a supportive nutrition guide to optimize individual performance.