Apparently 'Q' codes come from the days of morse code, where the use of standard questions helped to cut down message length. 'Q' therefore stands for question.
Example, 'QDM' would get you a magnetic bearing to a station, QTR would get you the correct time, etc.
QNH stands for what would my altimeter be reading if I were on your airfield above MSL, or the barometric pressure setting at that airfield.
Hope this helps.
Kermie
[ 07 August 2001: Message edited by: Kermit 180 ]