Gross thrust measures the amount of thrust produced when the aircraft is:

Gross thrust specifically refers to the total thrust produced by a jet engine at a given moment without accounting for any losses due to the aircraft's motion through the air. When the aircraft is stationary, as indicated in the correct choice, the engine is still able to produce maximum thrust as measured by the engine's thrust capability alone.

In this state, the aircraft is not influenced by dynamic conditions like airspeed, and the thrust produced is purely a result of the engine's internal mechanics when running at full power. This is fundamental in the evaluation of engine performance because gross thrust provides a baseline measurement that can later be adjusted for real-world conditions.

Other scenarios, such as when the aircraft is moving on the runway, at cruising altitude, or going through takeoff, introduce additional factors such as air resistance and engine efficiency related to airflow, affecting the net thrust available for actual propulsion. Thus, they do not accurately represent the gross thrust, which is precisely the measurement of thrust without these influencing variables.