the vertical distance of a level, a point, or an object considered as a point measured from mean sea level
Altitude is
Pressure Altitude (PA) is
the indicated altitude when an altimeter is set to ISA at sea level (1013), when set to 1013 the altimeter reads Flight Levels (FL)
the indicated altitude when an altimeter is set to ISA at sea level (1013), when set to 1013 the altimeter reads Flight Levels (FL)
Pressure Altitude (PA) is