Which of the following best describes "inaudible"?

The term "inaudible" specifically refers to sounds or speech that cannot be heard at all. This means that there is either no sound present or the sound is below the threshold of hearing for the listener. Inaudibility indicates an absence of sound or that its volume is too low for any discernible recognition.

In contrast, the other options present scenarios involving sound. Being "too loud to understand" implies that there is sound, but it is overwhelming and muddled, making comprehension difficult. "Soft yet clear" describes a sound that is faint but understandable, which is the opposite of inaudible. "Only partially heard" suggests that some sound is present, but not all of it is discernible, which again contradicts the definition of pure inaudibility. Therefore, the best description of "inaudible" is indeed that which cannot be heard at all.