Hazard sailing is a type of sailing that involves navigating through hazardous waters. It requires a high level of skill and knowledge, as well as the ability to make quick decisions in order to avoid potential dangers. The term 'REEF' is used to describe an area of shallow water or rocks that can be dangerous for boats to pass through. Reefs can be found in many different types of waters, and it is important for sailors to be aware of their location in order to safely navigate around them.