(Standard Generalized Markup Language) An ISO standard for defining the format in a text document. Widely used in the publishing industry, an SGML document uses a separate Document Type Definition (DTD) file that defines the format codes, or tags, embedded within it. Since SGML describes its own formatting, it is known as a "meta-language." SGML is a very comprehensive language that also includes hypertext links. HTML is an SGML document that uses a fixed set of tags, while XML is a simplified version of SGML. See HTML, XML and DSSSL.