Many adventure activities, like climbing and hiking, and even canoeing and whitewater, have difficulty classification scales associated with them. These classification systems are good to know and use because they help participants gauge whether or not their skill level matches the difficulty of the activity they are considering.
This can prevent more novice participants from getting dangerously outclassed and more expert participants from getting bored.
Many of the systems used in the U.S. are based on the Yosemite Decimal System (YDS) and they work roughly the same way.
Yosemite Decimal System (YDS)
Class 1 – Walking with a low chance of injury, hiking boots a good idea.
Class 2 – Simple scrambling, with the possibility of occasional use of the hands. Little potential danger is encountered. Hiking Boots highly recommended.
Class 3 – Scrambling with increased exposure. Handholds are necessary. A rope should be available for learning climbers, or if you just choose to use one that day, but is usually not required. Falls could easily be fatal.
Class 4 – Simple climbing, with exposure. A rope is often used. Natural protection can be easily found. Falls may well be fatal.
Class 5 – Is considered technical roped free (without hanging on the rope, pulling on, or stepping on anchors) climbing; belaying, and other protection hardware is used for safety. Un-roped falls can result in severe injury or death.