If something is described as "unintelligible," it is:

The description "unintelligible" refers to something that cannot be understood or made sense of. This term is often used to describe speech, writing, or any form of communication that is so unclear, confusing, or obscure that it fails to convey meaning effectively. When information is unintelligible, it may be due to poor expression, complicated language, or a lack of coherence. Thus, the correct understanding of this term aligns perfectly with the provided answer, portraying a clear contrast to the other options, which imply clarity, ease of understanding, and engagement—all of which stand in stark juxtaposition to the essence of being unintelligible.