Types of aviation altitudes:
Indicated Altitude – Altitude data shown on the altimeter using the current altimeter setting input by the pilot.
True Altitude – Height above mean sea level (MSL).
Absolute Altitude – Height above ground level (AGL).
Pressure Altitude – Indicated altitude when an altimeter is set to 29.92 in Hg and used primarily in performance calculations at high altitude flight.
Density Altitude – Pressure altitude corrected for nonstandard temperature variations.