Every profession has jargon and this is one of them in audiophile world. A practical definition of "neutral" imho is "all frequencies are measured in approximately similar sound pressure levels (SPL) within the specified tolerance between the low bass and high treble natural roll-of limits from a transducer in an anechoic setting." It sounds mouthful but several key phrases need be noted. First off, "similar sound pressure level" implies no drivers are perfectly linear and there is no perfect measurement method. As such, the measured SPL will fluctuate and no truely flat response curve exist in reality. Second, "within the specified tolerance" implies one needs to specify the tolerance interval, e.g., +-3dB, in order to render an objective assessment if a transducer is neutral. Third, "between the low bass and high treble natural roll-off limits" implies that we only assess the response curve bet. the natural roll-off limits of the high and low ends, again, within the specified tolerance. For example, we could still call the response curve neutral even there is steep roll off below the natural roll-off limit for bass. Often time, we see the mid-bass is boosted in order to get a better bass extension and the response curve will not be considered neutral if the boosted mid-bass exceeds to the specified tolerance. Lastly, the measurement needs to be conducted in an anechoic setting.
Sorry for being mouthful. Please advise if I mess up something. There is another jargon for you guys. What does "organic" sound mean?