Metadata is information about a GIS database. It describes several attributes about a particular database. Among those attributes are data quality, data content and data condition. The Federal Geographic Data Committee (FGDC) identifies three major uses of metadata. First, metadata helps to organize and maintain an organization's investment in data. Second, it provides information to data clearinghouses. Finally, metadata aids in data transfer.

The creation of metadata is a growing necessity as the amount of digital geospatial data and the number of producers of data increases. Because data development is the most expensive part of a GIS, metadata can help the user decide if an existing data set is useful for a particular GIS analysis.
Learn More about metadata at FGDC

• Developing Spatial Data Infrastructures: The SDI Cookbook Version 1.1
  This is a 150 page Spatial Data Infrastructure Implementation Guide which "includes data, metadata, catalog, services, and case studies on how to establish compatible systems within and between organizations to facilitate information discovery, applications support and exchange."
• Metadata Tools at FGDC
• NPS Data Store The NPS Natural Resource GIS Program has developed the NPS Data Store, a service-wide repository for spatial and non-spatial NPS metadata and data. The Data Store contains records for both spatial and non-spatial data sets including documents, natural resource databases, GIS data sets, boundary data, base cartographic data, GIS layer standards, and images. Posting data to the Data Store satisfies NPS data distribution requirements for data producers and provides access to a broad audience of data consumers both within and outside the NPS.
• NPS Metadata Tools & Editor The NPS Metadata Tools & Editor is a custom software application for authoring and editing National Park Service (NPS) metadata. It extends the basic functionality of ESRI's ArcCatalog for managing geospatial metadata and also provides a stand-alone version for creating and manipulating non-spatial metadata outside of ArcCatalog. The Tools & Editor is intended to be the primary editor for NPS metadata that will be uploaded to the NPS Data Store. While not specifically designed for users external to the NPS, the Tools and Editor features a number of powerful metadata editing capabilities that any metadata author is likely to find useful.
• National Spatial Data Infrastructure
• NPS GPS Data Dictionary FTP Site