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 is the principal strength and conditioning program for many police academies and tactical operations teams, military special operations units, champion martial artists, and hundreds of other elite and professional athletes worldwide.