data that provides information about other data
In other words, it is "data about data." wikipedia 
# Context We are working to create a new form of organisation of metadata. In this work we look to gather together around a practical project some of the best initiatives in this space.
# Classification of metadata
Metadata allows users to access resources through: > allowing resources to be found by relevant criteria, identifying resources, bringing similar resources together, distinguishing dissimilar resources, and giving location information.
Metadata of telecommunication activities including Internet traffic is very widely collected by various national governmental organizations. This data is used for the purposes of traffic analysis and can be used for mass surveillance.
In the 21st century, metadata typically refers to digital forms, but traditional card catalogs contain metadata, with cards holding information about books in a library (author, title, subject, etc.)
- wikimedia 
Metadata was traditionally used in the library catalog of library until the 1980s, when libraries converted their catalog data to digital databases. In the 2000s, as data and information were increasingly stored digitally, this digital data was described using metadata standards.
The 1st description of "meta data" for computer systems is purportedly noted by MIT's Center for International Studies experts David Griffel and Stuart McIntosh in 1967: "In summary then, we have statements in an object language about subject descriptions of data and token codes for the data. We also have statements in a meta language describing the data relationships and transformations, and ought/is relations between norm and data."
Unique metadata standards exist for different discipline (e.g., museum collections, digital audio files, websites, etc.). Describing the Content (media) and Context (computing) of data or computer file increases its usefulness.
For example, a HTML editor may include metadata specifying what software language the page is written in (e.g., HTML), what tools were used to create it, what subjects the page is about, and where to find more information about the subject.
This metadata can automatically improve the reader's experience and make it easier for users to find the web page online. A CD may include metadata providing information about the musicians, singers and songwriters whose work appears on the disc.
In many countries, government organizations routinely store metadata about emails, telephone calls, web pages, video traffic, IP connections, and cell phone locations.
# Metadata
> __Parents:__ Archive
# See also - Wiki Page Metadata - Linked Data
# Links
- Agris: International Information System for the Agricultural Sciences and Technology - Classification scheme - Crosswalk (metadata) - DataONE - Data Dictionary - Dublin Core - Folksonomy - GEOMS – Generic Earth Observation Metadata Standard - Geospatial metadata - IPDirector - ISO/IEC 11179 - Knowledge tag - Mercury: Metadata Search System - Meta element - Metadata Access Point Interface - Metadata discovery - Metadata facility for Java - Metadata from Wikiversity - Metadata publishing - Metadata registry - Metamathematics - METAFOR - Microcontent - Microformat - Multicam (LSM) - Observations and Measurements - Ontology (computer science) - Official statistics - Paratext - Preservation Metadata - SDMX - Semantic Web - SGML - The Metadata Company - Universal Data Element Framework - Vocabulary OneSource - XSD