As a competitive sport, Powerlifting is where athletes compete to attain the best single rep max squat, bench press, and deadlift. Powerlifting training is the process involved in getting there. Unlike other strength sports or fitness related activities, powerlifting involves specifically getting strong at the squat, bench press, and deadlift, so training is focus around improving those movements. It does not mean other movements and exercises are not performed, but a properly built powerlifting program should be based around helping an athlete achieve optimal strength levels in those 3 movements. All other exercises outside of those should be used to help aid in the strength development of the squat, bench press, and deadlift in some way.
Someone training for powerlifting does not necessarily have to compete in powerlifting competitions though. Someone may just have the desire of being strong, and there are not many better ways to do so than getting strong on the squat, bench press, and deadlift. So whatever someones competitive aspirations may be, the one thing that can be guaranteed is that powerlifting training is going to help them get stronger.