Metadata (also spelled meta data) refers to structured data that contain or define other data, making it more discoverable in online environments. Metadata also provides context to data and can make data easier to reuse and combine with other data. Metadata can also include information about the quality of the data.
Metadata may be totally innocuous, such as formatting instructions and margin determinations, but sometimes metadata provides crucial evidence that is not available in a paper document. Metadata may reveal who worked on a document, the name of the organization that created or worked on it, information about prior versions of the document, recent revisions, and comments inserted in the document during drafting or editing. . . . The hidden text may reflect editorial comments, strategy considerations, legal issues raised by the client or the lawyer, or legal advice provided by the lawyer. Metadata may provide information that a paper document would not provide or information that differs from a paper document. Metadata may also reveal that a document has been changed or backdated.
Metadata might include the source of the information, transformations producing the derived information, and even procedures to extract content. Although it is not practical to maintain all details about information provenance, metadata can provide a conservative subset. Metadata can be maintained at varying degrees of granularity, depending on the sensitivity and criticality of the information.