In aviation terminology, what does "NAC" stand for?

In aviation terminology, "NAC" stands for Non-Absolute Concentration. This term is used in various contexts such as the measurement of certain aviation-related parameters where the values are expressed in a manner that is not tied to absolute scaling. Non-Absolute Concentration can relate to concentrations of fluids, gases, or measurements that compare relative values rather than absolute quantities, which can be crucial in understanding aspects such as air quality, fuel performance, or environmental impacts during flight operations.

The other terms listed do not align with widely recognized aviation terminologies. Non-Aerodynamic Concentration, Non-Active Control, and Non-Adjusted Coefficient do not represent established concepts within the industry and thus are not relevant to the context of this question. Understanding the use of Non-Absolute Concentration can help aviation professionals effectively interpret and manage measurements critical to safety and performance in various aircraft systems.