Then there is QFE which is the pressure setting to apply to your altimeter to result in close to zero altitude indicated at the airfield datum.
The closest I can get to unscrambling QFE as though it is an acronym is Quick Find Earth!!
Airfield datum begs the question. Where normally is the airfield datum particularly in relation to the nominal GPS position or INS setting.
What other Qs relate to atmospheric pressure. I've forgotten because I don't think they matter much or have become obsolete.