A black diamond is a ski slope rating that indicates a challenging run for more advanced skiers who are more confident in their own skill level. It is one of the more difficult trails at a particular resort and is often one of the steepest on the hill. It may also be narrower than most of the other trails, requiring more frequent hairpin turns in order to control speed and positioning. Hazards may include cliffs, trees, and rocks.

A "no-fall zone" is a specific location on the mountain or trail where it is very clear that any potential fall could lead to very serious injury or destruction of equipment. It is usually located on some of the higher level trails on the mountain and is often used as a communication tool to encourage conservative skiing with a focus on skiing in control.

Therefore, a black diamond no fall zone would refer to a specific location on a black diamond ski slope where any potential fall could lead to very serious injury or destruction of equipment. It is a location that requires advanced skiing skills and experience to navigate safely.