(2)
AGL ALTITUDE - Altitude expressed in feet measured Above Ground Level.

(3)
INDICATED ALTITUDE - The altitude as shown by an altimeter. On a pressure or barometric altimeter it is altitude as shown uncorrected for instrument error and uncompensated for variation from standard atmospheric conditions.

ALTITUDE (JCS, NATO, ICAO) - The vertical distance of a level, a point or an object considered as a point, measured from mean sea level.
ALTITUDE READOUT/AUTOMATIC ALTITUDE REPORT - An aircraft's altitude, transmitted via the Mode C transponder feature, that is visually displayed in 100 foot increments on a radar scope having readout capability. (See Automatic Radar Terminal System, NAS Stage A, Alpha Numeric Display)
ALTITUDE RESERVATION/ALTRV (IFIM) - Airspace utilization under prescribed conditions normally employed for the mass movement of aircraft or other special user requirements which cannot otherwise be accomplished. ALTRVs are approved by the appropriate Federal Aviation Administration facility. (See Air traffic Control System Command Center. Refer to AP/2, Chapter 1, for EUCOM or AP/3, Chapter 1 for PACOM ALTRV Procedures).
(1) ALTRVs are classified as either moving or stationary.
(a)
A moving ALTRV will normally include the enroute and arrival phases of flight up to and including the arrival holding pattern at which Air Traffic Control provides separation between aircraft in accordance with FAA 7110.65.