- noun a webpage markup language that is a simplified version of the SGML system and allows a designer to create his or her own customised markup tags to improve flexibility.
- Abbreviation of Extensible Markup Language. A specification for the format of documents and data to be used on the Web. It is a scaled-down version of SGML, and seeks to retain the comparative simplicity of HTML, yet offer greater flexibility in areas such as organization and presentation, while being fully compatible with both. Also called XML format.