The upper-atmosphere is the part of earth's atmosphere that is above the homosphere (where all gases are well mixed) and starts at approximatly 100km. When asking questions specifically about the upper-atmosphere, use this tag and also include the [atmosphere] tag and [meteorology] tag if appropriate.
The upper atmosphere contains the thermosphere and exosphere. The Kármán line, or Karman line (100km) is commonly used to define the boundary between aviation and aerospace.
