CIRCA:Metadata
From CIRCA
What is Metadata?
To be brief and simple, metadata is "data about data", defined by OCLC (Online Computer Library Center) and NCSA (National Center of Supercomputing Applications). To be precisely, metadata is structured information that describes, explains, locates, or otherwise make it easier to retrieve, use, or manage an information resource.
Metadata has been applied in many fields, and each of which has a unique definition of metadata. So there isn't an agreed definition that describes all kinds of metadata used in every field.