The Standard Generalized Markup Language (SGML) is a markup language for documents. SGML is a standardized development from IBM's "Generalized Markup Language" GML, developed in the 1960s by Charles Goldfarb, Edward Mosher and Raymond Lorie (whose surname initials also happen to be GML).
SGML provides a single markup syntax that can be used for many applications. This prevents the need for multiple application-specific markup languages.
SGML was originally designed to enable the sharing of machine-readable documents in large projects in government and the aerospace industry. It has also been used extensively in the printing and publishing industries.
SGML syntax example:
<QUOTE TYPE="example"> typically something like <ITALICS>this</ITALICS> </QUOTE>
SGML is an ISO standard: "ISO 8879:1986 Information processing -- Text and office systems -- Standard Generalized Markup Language (SGML)"
SGML is very flexible and powerful, but its complexity has prevented its widespread application for small-scale general-purpose use. XML is an attempt to simplify SGML for general-purpose applications, such as the semantic web.