True airspeed can be defined as:

True airspeed is defined as calibrated airspeed that has been corrected for the effects of altitude and nonstandard temperature. This measurement is crucial for pilots because it reflects the actual speed of the aircraft relative to the surrounding air, which is influenced by changes in atmospheric pressure and temperature at different altitudes.

At higher altitudes, the air density decreases, which can cause indicated airspeed (the speed displayed on the aircraft's airspeed indicator) to underestimate the actual speed through the air. By applying the appropriate corrections for both altitude and nonstandard temperature, pilots can derive true airspeed from calibrated airspeed. This information is vital for flight planning and performance calculations, as it allows pilots to accurately assess their aircraft's capabilities in various flight conditions.

Understanding true airspeed helps in achieving precise navigation, fuel consumption calculations, and ensuring safety by managing aircraft performance adequately while climbing, cruising, and descending.