CrossFit is many things. Primarily, it’s a fitness regimen developed by Coach Greg Glassman over several decades. He was the first person in history to define fitness in a meaningful, measurable way (increased work capacity across broad time and modal domains). CrossFit itself is defined as that which optimizes fitness (constantly varied functional movements performed at relatively high intensity). CrossFit is also the community that spontaneously arises when people do these workouts together. In fact, the communal aspect of CrossFit is a key component of why it’s so effective.
CrossFit in 100 words by Greg Glassman: Eat meat and vegetables, nuts and seeds, some fruit, little starch and no sugar. Keep intake to levels that will support exercise but not body fat. Practice and train major lifts: Deadlift, clean, squat, presses, C&J, and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-ups, presses to handstand, pirouettes, flips, splits, and holds. Bike, run, swim, row, etc, hard and fast. Five or six days per week mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense. Regularly learn and play new sports.