In information systems, a tag is a keyword or term assigned to a piece of information. This kind of metadata helps describe an item and allows it to be found again by browsing or searching. Tags are generally chosen informally and personally by the item's creator or by its viewer, depending on the system, although they may also be chosen from a controlled vocabulary.

Metadata is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including:Descriptive metadataThe descriptive information about a resource. It is used for discovery and identification. It includes elements such as title, abstract, author, and keywords. Structural metadataMetadata about containers of data and indicates how compound objects are put together, for example, how pages are ordered to form chapters. It describes the types, versions, relationships, and other characteristics of digital materials. Administrative metadataThe information to help manage a resource, like resource type, permissions, and when and how it was created. Reference metadataThe information about the contents and quality of statistical data. Statistical metadataAlso called process data, may describe processes that collect, process, or produce statistical data. Legal metadataProvides information about the creator, copyright holder, and public licensing, if provided.