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Metadata is the information used in and specifying the uses and characteristics of cryptographic keys in a cryptographic key management system. Metadata may include: the key owner, the PKI service, key usage, the validity period, key parameters, etc.


Metadata have been interpreted to exclude the subject line. Other types of communications have different metadata elements.[1]


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 is

a subset of data, and are data about data. Metadata summarize data content, context, structure, interrelationships, and provenance (information on history and origins). They add relevance and purpose to data, and enable the identification of similar data in different data collections.[2]
the descriptive information about data that explains the measured attributes, their names, units, precision, accuracy, data layout and ideally a great deal more. Most importantly, metadata includes the data lineage that describes how the data was measured, acquired or computed.[3]
information generated by our communications devices and our communications service providers, as we use technologies like landline telephones, mobile phones, desktop computers, laptops, tablets or other computing devices. It is essentially information about other information. . . .[4]
structured information that describes, explains, locates, or otherwise makes it possible to retrieve, use, or manage an information resource. In the cultural heritage community, metadata are often broken into three classifications: administrative, structural, and descriptive.[5]


In connection with websites, metadata is information that describes the attributes or search keywords that have been embedded in a Web page's source code.

Telephone communications[]


includes the calling and called telephone numbers, the time and duration of a call, but not its content."[6]


Pieces of metadata or traffic data are the digital crumbs that we leave behind when we use communications technologies and online services. Metadata includes information that reveals the time and duration of a communication, the particular devices, addresses, or numbers contacted, which kinds of communications services we use, and at what geolocations. And since virtually every device we use has a unique identifying number, our communications and Internet activities may be linked and traced with relative ease — ultimately back to the individuals involved. All this metadata is collected and retained by communications service providers for varying periods of time, including by telecommunications companies and Internet Service Providers, for an array business purposes.[7]

Metadata includes a formal description of the data, as well as information on how to acquire the data, and information for using the data, such as accuracy, security, and rights. Metadata provide the scientific, technical, contextual, representational, provenance, and other information necessary to enable creative re-use and re-purposing 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.[8]

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.


  1. Bulk Collection of Signals Intelligence: Technical Options, at 3 n.6.
  2. National Science Foundation, Cyberinfrastructure Council, Cyberinfrastructure Vision for 21st Century Discovery 22 (Mar. 2007) (full-text).
  3. Jim Gray, Scientific Data Management in the Coming Decade 2 (Jan. 2005) (full-text).
  4. A Primer on Metadata: Separating Fact from Fiction, at 3.
  5. ARSC Guide to Audio Preservation, App. B, at 226.
  6. Bulk Collection of Signals Intelligence: Technical Options, at 3 n.6.
  7. Id.
  8. Jennifer M. Smith, "Electronic Discovery and the Constitution: Inaccessible Justice," 6 J. Legal Tech. Risk Mgmt. 122, 138–39 (2012) (ellipsis in original) (footnotes omitted).

See also[]