I think it's a new slang term for greek also known as backdoor entry.
The Avalanche Terrain Exposure Scale (ATES) was developed by Parks Canada to help backcountry users assess the severity of the terrain encountered in a given trip. It has three terrain classes that describe the exposure of terrain to potential avalanche hazard. ATES ratings are compiled by professionals who consider eleven weighted terrain parameters in ranking a trip or tour as Simple, Challenging, or Complex.
