Metadata is commonly defined as data about data. Broadly, this means information about a document and its content. While the primary aim of metadata is to improve resource discovery, metadata sets are also being developed for other reasons, including: administrative control, security, personal information, management information, content rating, rights management and preservation. While this topic concentrates on resource discovery and retrieval, these additional purposes for metadata should also be kept in mind.

The metadata record can be linked to the Web page it describes in one of the two following ways:

1. metadata may be contained in a separate file from the Web page, as in the case of the Corporate Document Repository;
2. metadata may be embedded in the resource itself, as in the case of encoded metadata within a Web page.

Many metadata standards in use today, including the Dublin Core and AgMES standards, do not prescribe either type of linkage, leaving the decision to each particular implementation.