The clean and jerk is a composite of two weightlifting movements, most often performed with a barbell: the clean and the jerk.
During the clean, the lifter moves the barbell from the floor to a racked position across the deltoids. During the jerk the lifter raises the barbell to a stationary position above the head, finishing with straight arms and legs, and the feet in the same plane as the torso and barbell.
Of the several variants of the lift, the most common is the Olympic clean and jerk, which is contested in Olympic weightlifting events.
To execute a clean, a lifter grasps the barbell just outside the legs, typically using a hook grip. Once the barbell is above the knees, the lifter extends explosively, raising the bar as high as possible before quickly dropping into a squat and receiving it in a “racked” position in front of the neck and resting on the shoulders. To complete the clean, the lifter stands, often propelling the bar upward from the shoulders slightly as the erect position is attained and shifting the grip slightly wider and the feet slightly closer together in preparation for the jerk.
The jerk begins from the “front rack” position, which is the finishing position of the clean. The lifter dips a few inches by bending the knees, keeping the back vertical, and then explosively extends the knees, propelling the barbell upward off the shoulders, and then quickly dropping underneath the bar by pushing upward with the arms and splitting the legs into a lunge position, one forward and one back. The bar is received overhead on straight arms, and, once stable, the lifter recovers from the split position, bringing the feet back into the same plane as the rest of the body.
Taken from Wikipedia.