Easy: Generally it is to understand between 900 and 2000 meters (3000-6500 feet) altitude with plenty of ups and downs trails. Trekkers no need to be sportive but a good physical condition is required to enjoy this experience.
Moderate: It may involve side trips to higher elevation between 900m to 3000m, close to the trees line in the Himalayan valley.
Moderate+: Reasonably demanding trekking at altitude up-to 4200 meters with trips to higher elevations and could include treks away from villages on ill-defined mountain trails, trekkers need to have regular walking experiences to enjoy such trekking adventure .
Strenuous: Treks of demanding nature, require all participants to be physically fit and in excellent health condition. The trail often passes by remote alpine areas and sometimes reaching altitudes up to 5500 meters (18000 feet) and High Mountain passes.
Alpine: These are extremely demanding treks, sometimes in very remote areas on rough terrain, and could include (in Nepal) climbs of one or more of the "trekking peaks" (maximum altitude, Mt. Mera at 6461 meters, 21192 feet). Participants should have at least basic mountaineering skills, first time climbers may be accepted on some of the "easy" routes but Medical certificates are required for acceptance into these climbing treks.