Tinnitus is best described as:

Tinnitus is defined as the perception of sound in the absence of an external auditory stimulus. This perception can manifest as ringing, buzzing, hissing, or other types of noise and can vary in intensity and duration for different individuals. It is essential to note that tinnitus is not an actual sound produced in the environment but rather a subjective experience that can occur due to various underlying causes, such as hearing loss, exposure to loud noises, or other health conditions.

The other options, while they touch on related auditory topics, do not accurately encapsulate the essence of tinnitus. For instance, a lack of ability to hear high frequencies is related to hearing loss, not tinnitus itself. Similarly, tinnitus is not classified as a hearing test nor is it directly caused by earwax, although excessive earwax can lead to hearing issues that might be associated with tinnitus in some cases. Thus, the most accurate and comprehensive description of tinnitus is that it involves the perception of noise without any external source.