Free text is the traditional definition of unstructured data (along with audio & video equivalents). But I agree with GP, that people usually mean inconsistently-structured data when they use the term, whether it's accurate or not.
Free text being the definition of unstructured data is kind of funny if you think about it (and I agree that amongst computer people that's how they think about it), since the whole point of text is to structure data using alphabets, syllabary or logograms, such that it can be meaningfully be transferred and understood by multiple biological interpreters :)