The squat is a lower body exercise used in strength training. It is also a competitive lift in powerlifting and an essential movement in the sport of weightlifting. The exercise's main emphasis is on the quadriceps and the glutes, but it also involves the hamstrings, the calves, and the lower back. The squat is often called "the king of exercises" by those who believe it capable of inducing more and faster muscle growth than any other exercise. 
The squat is performed by bending the legs at the knees and hips, lowering the torso between the legs, and then reversing direction to stand up straight again. The torso remains relatively upright throughout the movement. It acts as a supporting structure, unlike its role in the deadlift. Proper technique is critical, otherwise very serious injuries or gradual injury over a period of time can occur. The back must maintain its natural curvature and not "round out" (excessive lumbar or thoracic kyphosis), otherwise excess strain can be placed on the spine and cause serious injury. Lifting belts can be used to help support the lower back.
The feet should be flat on the floor, with even distribution of weight between the heel and the ball of the foot during eccentric muscle action. In order to reach a range of motion beyond parallel, individuals without sufficient ankle flexibility may try putting a flat board beneath the heels to artificially improve their flexibility. Similarly, a wedge shaped board may be used, allowing the entire foot to remain in contact with a single surface, improving stability over the first technique. Both methods are short-term fixes and require that regular stretching and a full range of motion be employed to maintain and increase flexibility to the desired levels with the ultimate aim that the board's use be eliminated. In the sport of weightlifting, a specifically designed shoe, that has a heel elevated by an encased wooden block, is commonly worn. Some experts discourage the use of a board or heel, however, because it may lead to a breakdown of proper form. In any squat, even one performed without these depth-increasing aids, the lifter should take care to exert force from the heel of the foot and not from the toes during concentric muscle contraction in order to maintain balance and keep the focus on the muscles of the thigh.
To avoid the chance of getting stuck under the bar, heavy barbell squats are best performed either inside a power cage or in the presence of one or more spotters, who can help to safely return the barbell to the squat rack at the end of the set if the lifter is unable to do so. A smith machine can also be used, though the movement is less natural than with a bar, and may lead to joint problems.
On the 16th December 2007, Dr Thienna Ho from Vietnam performed 5,135 sumo squats in one hour. 
The squat has a number of variants, some of which can be combined (e.g. a dumbbell split squat):
- In the Squat or Powerlifting Squat, the bar is held anywhere over the back of the neck, within the rules, and feet placed wherever the lifter chooses for the squat for what is best for him.
- In the back squat, a barbell is held across the upper back.
- In the front squat, the weight (usually a barbell) is held in front of the body across the clavicles and deltoids in either an Olympic grip, as is used in weightlifting, or with the arms crossed and hands placed on top of the barbell.
- In the Olympic Squat, the bar is placed for a front squat or back squat position. front squat with a clean grip and back squat with a high-bar position. On both occasions the feet placed roughly in clean receiving position. The lift is done up to a weight of 25 % greater than the athletes clean and jerk on both lifts (for a professional, others may differ.) and the style is designed to only benefit Olympic weightlifting.
- In the overhead squat, a barbell is held overhead in a wide-arm snatch grip; however, it is also possible to use a closer grip if flexibility allows.
- In the dumbbell squat, the weight may be held hanging from the side (suitcase position), vertically at the chest (goblet position), or above the head with the arms extended (waiter position).
- In the dumbbell front squat, the weights are held resting on the shoulders.
- In the box squat, the lifter sits back onto a short box, momentarily relaxing the hip flexors, before contracting them and rising off the box; the use of a box sets a consistent depth and increases emphasis on the muscles of the posterior chain.
- In the Zercher Squat, the weight is held in the crook of the elbows against the chest.
- In the Hack squat, a barbell is held in the hands just behind the legs; it was invented by early 1900s professional wrestler Georg Hackenschmidt.
- In the sissy squat, a dumbbell is held behind the legs while the heels are lifted off the ground and the torso remains flat while the lifter leans backwards; sometimes done with a plate held on the chest and one arm holding onto a chair or beam for support.
- The pistol squat is a freestanding one-legged squat where the non-lifting leg is held in free space.
- The split squat is an assisted one-legged squat where the non-lifting leg is rested on the ground a few 'steps' behind the lifter, as if it were a static lunge.
- The Bulgarian squat is is a squat performed much like a split squat, but the foot of the non-lifting leg is rested on a knee-high platform behind the lifter.
- The Hindu squat is a squat done without weight where the heels are raised and body weight is placed on the toes; the knees track far past the toes.
- The jump squat is a plyometric exercise where the squatter jumps off the floor at the top of the lift.
- The air squat is a squat done with no weight or barbell, often at higher repetitions than other variants.
The squat also has a number of commonly specified depths:
- The quarter squat descends about half of the way down towards a half squat.
- The hams parallel squat descends until the bottom of the thighs, the hamstrings, reach an imaginary line drawn parallel to the floor.
- The quads parallel or powerlifting legal squat descends until the crease of the top of the thighs at the hips is lower than the tops of the knees.
- The half or thighs parallel squat descends to a depth that is between hams-parallel and quads-parallel. The whole leg is parallel to the ground.
- The full or ass to the grass/ground (ATG) squat descends past quads-parallel to the maximum that a lifter's flexibility allows. This is the common depth for Olympic weightlifters, as receiving the weight from a clean, usually ends up at the deepest point.
Squatting below parallel qualifies a squat as deep while squatting above it qualifies as shallow.
- Sidney, D: "Squat today, grow every day: do this king of all exercises and sprout muscle even in your upper body - Body Shop". Men's Fitness, April 2005.
- The Insider's Tell-All Handbook on Weight-Lifting Technique. Stuart McRobert, CS Publishing; 2nd edition, September 1999 - Book Excerpt
- Russi Sarnataro, B (2006-05-19). 9 Least Effective Exercises. WebMD. Retrieved on 2008-02-04.
- New record for Sumo Squats - December 16th 2007 - Guinness World Records Site
- Louie Simmons' (of Westside Barbell) Description