What Does Metadata mean

I'm i the middle of writing the book (along with Mark) and I was using the word Metadta alot. Then something happened on a client project which made me realise that few people probably understand what this word actually means.

The OraFaq makes a good start
"Data that is used to describe other data"

But does that clear it up?

How about
"Metadata is information about a particular data set which may describe, for example, how, when, and by whom it was received, created, accessed, and/or modified and how it is formatted. Some metadata, such as file dates and sizes, can easily be seen by users; other metadata can be hidden or embedded and unavailable to computer users who are not technically adept"

Every other definition I see just says "Data about data"

So that clears it up then!