I never knew either and always got confused, so I just made up my own definitions.
QNH = Quoted Nautical Height i.e. Nautical being sea level.
QFE = Quoted field elevation i.e height above field
QDM = Quoted direction Magnetic
QDR = Quoted Direction Recipricol
No scientific basis, but It got my head round the ones I was interested in.
Not really answered the question either. Sorry for wasting bandwidth.
