From Science Europe Data Glossary
Definition: Unstructured data usually refers to information that does not reside in a traditional row-column database or spreadsheet. It is the opposite of structured data — the data stored in fields in a database.
Explanation: Unstructured data files include text and multimedia content, such as the content of e-mail messages, word processing documents, videos, photos, audio files, presentations, webpages and many other kinds of business documents. Note that while these sorts of files may have an internal structure, they are still considered "unstructured" because the data they contain does not fit neatly in a database of rows and columns.
See also: Structured data