A short term for "permanently frozen ground"; any part of the earth's crust, bedrock, or soil mantle that remains below 32ºF (0ºC) continuously for a number of years
National Wildfire Coordinating Group (NWCG), Glossary of Wildland Fire Terminology, NWCG Program Management Unit, National Interagency Fire Center, Boise, ID, USA 2014. http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf, (For Fr - Amer) {45}