Meta-data
Any data that describes other data. For example, search keywords describing a web page or tags for a blog entry are metadata. Using this page as an example, "metadata, meta, data, meta-data, computer, dictionary, jargon, term, glossary, define, about" are all keywords that describe this page. Alone these words are meaningless; however, all these words combined give a basic understanding of what the page is about.
Also see: Meta-character