This page explains is pretty well, I too was unaware of this until a few months ago.
Week 26: Module 3 Exams & New Zealand - Pilot George, CTC Aviation Cadet Blog
Basically, 85% average will ensure you're eligible for
most airlines in the hold pool. Less than 85% and you may be excluded from some airlines. Similar requirements exist for the flying side of training.
I'd stress that I'm just repeating information from other sources, checking with CTC directly is probably the best way to go.