Unintelligent means exactly what it sounds like it means––not intelligent, not smart. Someone who is unintelligent might not be able to read this sentence, or they might just not get it if they do.
Don't confuse unintelligent with unintelligible. Unintelligible means something that cannot be understood. Some doctors have handwriting so messy as to be considered unintelligible, but that doesn't mean they're unintelligent. If your cell-phone signal is weak, you might find that what your mom is telling you on the phone becomes unintelligible to you — but that doesn't make you unintelligent.
