Standard Generalized Markup Language. The international standard for specifying the structure and content of electronic documents. SGML is used for the markup of data in a way that is self-describing. SGML is not a language but a way of defining languages that are developed along its general principles. A subset of SGML called XML is more widely used for the markup of data. HTML (Hypertext Markup Language) is based on SGML and uses some of its concepts to provide a universal markup language for the display of information and the linking of different pieces of that information.