CrossFit is a strength and conditioning workout style made up of functional movements performed at high intensity levels. These physical movements are actions that you usually perform in your daily life, like pulling, pushing, squatting etc.
This workout uses different equipment to accomplish fitness, like rowers, ladder, medicine balls, battle ropes and so on.
CrossFit is extremely modifiable for all fitness levels, so it can be designed anyway to train anybody from youngsters to elderliness where crossfit is way more effective when compared to walking or jogging.