Indicated altitude is defined as:

Indicated altitude is defined as the altitude read directly from the altimeter, which measures atmospheric pressure. The altimeter is calibrated for standard atmospheric conditions and translates changes in pressure into altitude readings. When a pilot or dispatcher refers to indicated altitude, they are referencing this direct reading, which is essential for navigation, safety, and maintaining the appropriate separation between aircraft.

This definition is vital for understanding how aircraft operate within the airspace. The altimeter can be affected by factors such as temperature and atmospheric pressure variations, but the indicated altitude itself is specifically linked to the reading that pilots see on their instruments without adjustments for those variations.