This document defines SGML and discusses its advantages and disadvantages. SGML stands for Standard Generalized Markup Language, which is a system for organizing and tagging elements of a document. It allows authors to markup documents with structural, presentational, and semantic information. Some advantages of SGML include its flexibility, separation of content from appearance, and support of different media types. However, SGML also has disadvantages such as complex DTDs, linking, and software development.