For example, metadata would document data about data elements or attributes, (name, size, data type, etc) and data about records or data structures (length, fields, columns, etc) and data about data (where it is located, how it is associated, ownership, etc.). Metadata may include descriptive information about the context, quality and condition, or characteristics of the data. It may be recorded with high or low granularity.

Difference between data and metadata

Usually it is not possible to distinguish between (plain) data and metadata because:

    * Something can be data and metadata at the same time. The headline of an article is both its title (metadata) and part of its text (data).
    * Data and metadata can change their roles. A poem, as such, would be regarded as data, but if there is a song that uses it as lyrics, the whole poem could be attached to an audio file of the song as metadata. Thus, the labeling depends on the point of view.

These considerations apply no matter which of the above definitions is considered, except where explicit markup is used to denote what is data and what is metadata.

http://en.wikipedia.org/wiki/Metadata