Look up: high-altitude

1. 
   High altitude
   High altitude: Altitude sickness occurs at high altitude. So what is high altitude? Altitude is defined on the following scale: High altitude: 8,000 - 12,000 feet (2,438 - 3,658 meters); Very high altitude: 12,000 - 18,000 feet (3,658 - 5,487 meters); and Extremely high altitude: 18,000+ feet (5,500+ meters). Most people can go up to 8,000 feet (2, ...
   Found on http://www.medterms.com/script/main/art.
   
   
2. 
   High altitude
   `High altitude` are regions on the Earth's surface (or in its atmosphere) that are high above mean sea level. The composition and temperature of the atmosphere at high altitude is substantially different than at sea level. These differences can affect living organisms, including humans. High altitude is sometimes defined to begin at 1500 m above sea level. At high altitude, atmospheric pressure is lower compared to sea level. This is due to two ...
   Found on http://en.wikipedia.org/wiki/High_altitu