No Rep
A rep that didn't meet the movement standard and doesn't count.
What it means in a class
If a rep falls short of the standard — squat not deep enough, chin not over the bar, elbows not locked out — a coach or judge will call 'no rep' and you repeat it.
It isn't a telling-off. Consistent standards are what make scores comparable and, more importantly, what keep your movement safe as loads and speed increase.