The Alititude We read when We have set Correct(Current)QNH.This Alititude is Above Mean sea Level and the term ALTITUDE is used for it.
It is indicated Altitude Corrected for instrument and position Error.
The Altitude We read When We have set QNE(29.92),This Alititude is above Standard MSL and the Term FLIGHT LEVEL is used for it.
It is P.A Corrected for Non-Standard Temprature.
The Actual Altitude of the ACFT Above Ground Level(AGL).
You can read this Altitude When we have set QFE below the ACFT,and the term HEIGHT is used for it.
The Actual Altitude of Any object Above MSL like Mountain elevation and TV Antnna.
in 2 Condition We read True Altitude in the ACFT,one is on the ground,When We have set Correct QNH and we read elevation wich is True Alititude.
The other is in flight when we have set correct QNH and standard Atmospheric conditon exists.