Upper limit for which the aircraft is designed. The manufacturers take an cross section of people and I believe it is supposed to fit 90% of people, so the upper and lower 5% are excluded - not company discrimination, but manufacturing constraints. Guess if you have a problem you could request a special measurement to ensure that you aren't too tall in any particular area that could affect performance (ie hips to head). If you are 6'4'', you may just fit.