CrossFit is a high-intensity fitness program that uses bodyweight exercises and functional movements to build strength across all parts of the body. It involves constantly varied, full-body workouts that incorporate exercises like pull-ups, push-ups, squats, and movements using weights like snatches and deadlifts. CrossFit has grown significantly in popularity since the 2000s due to the benefits it provides, such as improved conditioning, versatility in physical abilities, and the ability to continuously challenge the muscles and prevent plateaus from occurring.