A metalanguage used to describe markup languages, such as Hypertext Markup Language (HTML). SGML can be used to describe the structure and elements of a document and the tags that will be used to display those elements in a document. SGML supports the creation of documents that are platform- and application-independent and that, therefore, retain their information formatting, indexing, and linkages. SGML is standardized by the International Organization for Standardization (ISO) as ISO 8879:1986. The Extensible Markup Language (XML) is essentially a condensed version of SGML. See also XML.