What is a repetition in weight training?

Answer 1

A repetition in weight training would be more than one lifting motion.

If I was doing 8 repetitions (aka reps) on squat, I would squat with the bar 8 times. Usually you do so many sets with a set amount of repetitions.

Answer 2

A repetition (or rep) is a single time that you do a specific exercise from start to finish. For example, if you are doing a squat: lowering your body until your thighs are parallel to the floor, then pushing back to your starting position is one rep.

A set is made up of reps. For example, if you've completed 12 squats and then repeated those twelve squats two more times, you have completed 3 sets of 12 repetitions.