Differentiate between Structured and Unstructured data?

Think of structured data a bit like filling in a form - each item goes in a fixed location, probably subdivided in to categories or sections.

Unstructured is like making notes on plain paper; even if all the same data, the ordering may not always be the same, a different number of lines depending how many things were noted or would have been blank.

Reading a structured data record loads each item in to a fixed part of your data structure; you do not have to try and figure out what item value relates to what title etc.