In helicopter terms, what does the term "Chord" specifically reference?

The term "Chord" in helicopter terminology specifically refers to the length of the Chord Line. The Chord Line is an imaginary straight line that runs from the leading edge to the trailing edge of the rotor blade. This measurement is an essential aspect of aerodynamics as it helps determine the overall aerodynamic profile of the rotor blades.

Understanding the chord length is important for pilots and engineers alike, as it influences various aerodynamic characteristics, including lift and drag. By knowing the length of the chord, one can calculate the aspect ratio of the blades and assess the performance of the rotor system. This fundamental knowledge has practical applications in both piloting and rotorcraft design, such as optimizing performance and efficiency during flight.

The other choices pertain to different aspects of rotorcraft performance or design but do not accurately define what "Chord" means in this context. Thus, the reference to "Chord" specifically relates to its measurement, making the choice about the length of the Chord Line correct in this question.