RE: Powerlifting --- Bodybuilding
Powerlifters lift to improve their limit strength performance in the squat, bench press and deadlift.
Bodybuilders lift in order to achieve a certain aesthetic ideal.
Powerlifters will tend to employ low reps (1-5) because these are better suited to improving limit strength than higher reps. Although they might sometimes use higher reps, including with a view to getting bigger, this will still be to the end of improving their powerlifting performance, often because they will do better in a higher weight category.
Powerlifters tend to lift to failure only rarely, since it is generally counterproductive for gaining strength. Their work sets will usually be in the area of 75%-90%, and usually toward the upper end of that range.
Bodybuilders willl employ higher reps (6-12) because that is the range in which protein fibres are broken down most efficiently in order for them to be rebuilt- hence hypertrophy. They have the added headache of having to watch what they eat- especially (or for some, exclusively) when they need to diet for a competition, which will require bodyfat of around 5% and less. A powerlifter doesn't have to concern himself with that except with a view to remaining in a weight class. BBers' work sets will tend to be in the region of 70%-85%, usually toward the lower part of that range.
Basically "What's the difference?" is not a good question. "What's the similarity?" would be better- and the answer is "They both lift weights."