Metadata is structured information that describes, explains, locates, or otherwise makes it easier to retrieve, use, or manage an information resource. (NISO 2004, ISBN: 1-880124-62-9, http://www.niso
.org/publications/press/UnderstandingMetadata.pdf)
a discrete unit of metadata (ISO 19115), an attribute of a metadata entity. A metadata element contains some content specifying the value of the element.
A collection of registered metadata records, maintained by a metadata registry. (ISO 11179). A kind of [Data Element](https://n2t.net/99152/h1083) that contains metadata.