Muddiest point for 10/4/2010

I have a question about unstructured data.  An example of unstructured data  is pure text which includes implicit structures.  But isn't the whole point of unstructured data that it is not defined?  In terms of implicit structure for the pure text, does that mean how writing in English has structure in terms of letters making words, words making ideas, and spaces to signify a pause? Or is it something else that implicitly structures pure text?  Does pure text have to be written in formal English or rather in a way that ideas are conveyed?