Definition: Metadata is literally “data about data”. For digital files, all of the information that describes and specifies the files that are broadcast on the Web without being indirectly displayed. This makes it possible to characterize and structure other data (whether physical or digital) There are many kinds of metadata: a photograph may be accompanied by metadata specifying the name of the photographer, the date of shooting, the conditions of protection related to intellectual property rights; a text can be accompanied by keywords, a tag web page. The use of metadata facilitates the classification of digital resources or their referencing by search engines, as it also helps organize the protection of files distributed with Digital Right Management (DRM) systems. Metadata is the basis of semantic web and archiving techniques.