Powerlifting is a pure strength sport -- a test of one's ability to move as much weight as possible in three different exercises: the squat, the bench press and the deadlift. Together those three movements constitute a full powerlifting meet, notes USA powerlifting, one of the biggest powerlifting federations in the country. However, you can choose not to compete in some of the events. If you only compete in the bench press and deadlift, you are participating in a pull/push competition.
The terms "pull" and "push" when referring to the deadlift and bench press come from the nature of the movements. A deadlift is considered a pull because you are pulling weight off of the ground and standing up with it. A bench press is considered a push because you are pushing weight away from you.
Together these movements work every muscle in the body. A deadlift works the quadriceps, glutes and hamstrings in the lower body. In the upper body it works the pulling muscles of the back -- such as the latissimus dorsi -- the muscles along the sides of your back -- including your trapezius -- and your lower back. A bench press works the pushing muscles in the upper body, namely the chest, shoulders and triceps.
In a full powerlifting competition, you perform the squat, bench press and deadlift. You are allowed three attempts for every exercise, according to the United States Powerlifting Association's rule book. From those three attempts, you take the highest amount of weight you lifted per exercise and total those three numbers together to get your overall total. The highest total wins.
Since strength is influenced by your total body weight, powerlifting meets are divided by weight classes, so you only have to compete against people who are roughly the same size as you. The International Powerlifting Federation has eight weight classes that break up the competition. This makes the meet more fair and competitive.
Why Not Squat?
Purposefully opting out of the squat in a powerlifting meet might seem like a bad idea. After all, there are only three exercises that you can add to your total at the end of the meet, so why would you only do two exercises? Sometimes there are pull/push powerlifting meets that don't include the squat. Another possibility is that someone can't squat due to an injury or they simply want to focus their energy on the bench press and deadlift.
The squat and deadlift are relatively similar movements because they both involve a lot of lower body and back strength. However, they are different enough that an injury impeding one exercise might not affect the other. For instance, a knee injury from squatting might not affect the deadlift because there isn't as much knee range of motion in that exercise. In that case, the powerlifter might decide to compete in the lifts that they can do because they can still do well.
The Purpose of Powerlifting Competition
Powerlifting is a strange sport because there are two competitions. There is one competition between opposing powerlifters who are trying to lift more than each other, and another competition against oneself. The goal of a powerlifting meet is not only to beat the competition, but to lift more weight than you ever have before. That's called a PR, or personal record, and most powerlifters strive for that in a meet.
Even if you don't compete in the squat, you can still break your own personal record in the bench press and deadlift during the meet. Some powerlifters find that more rewarding than winning an entire meet. In that way, powerlifting is more similar to marathon running. Not everyone goes into a marathon expecting to win the entire race, they signed up because they wanted to achieve a certain goal, whether that be completing the marathon in a certain amount of time or simply finishing the race.