The correct definition of vertical distance above the standard datum plane is known as:

The definition of vertical distance above the standard datum plane is best captured by pressure altitude. This term refers specifically to the height of an aircraft or object when measured from a standard reference point, which is set by the International Standard Atmosphere (ISA). The standard datum plane is defined as sea level in the absence of weather effects, making pressure altitude a crucial measurement in aviation as it helps pilots and air traffic controllers ensure safe and accurate altitude reporting.

Pressure altitude is determined by referencing the standard atmospheric pressure (29.92 inches of mercury) at sea level, regardless of the actual weather conditions. This standardization is essential for maintaining uniformity in altitude reporting among pilots, regardless of their geographical location or the varying atmospheric conditions they may encounter.

The other options refer to different altitude concepts. Indicated altitude is what the altimeter reads directly and may vary due to non-standard atmospheric conditions. True altitude is the actual height above sea level, which may differ from pressure altitude due to local atmospheric variations. Absolute altitude refers to the height above the terrain or ground level. Understanding these distinctions in altitude types is crucial for interpreting altitude data accurately in aviation contexts.