Used in the context of digital spatial data, metadata is the background information which describe the content, quality, condition, and other relevant characteristics of data. Metadata help a person to locate and understand data. For example a map legend is a pure metadata. The legend contains information about the publisher of the map, publication date, the type of map, a description of the map, spatial references, the map's scale and its accuracy, among many other things.
Metadata are simply that type of descriptive information applied to a digital geospatial file.
They are a common set of terms and definitions to use when documenting geospatial data. In a nutshell, metadata answer who, what,when,where, and how about every aspect of the spatial data. FGDC promotes the coordinated development, use, sharing, and dissemination of geographic data. Additional Federal agencies participate on FGDC subcommittees and working groups. The Department of the Interior chairs the committee.