Information is the operative term.
SGML provides an internationally recognized, non-proprietary language for designing your own markup schemes. Markup , broadly speaking, is character text or binary codes 'added to' data content in order to convey particular information about that data. In a document produced by a typical word processor file, markup is represented by the proprietary codes that the software inserts into the files to indicate which words should be printed in a certain font, which paragraphs should be centered, where page breaks occur, etc. In the case of a database system, markup is represented by proprietary codes in the data file which indicate where one field or record ends and another begins, and so on. Markup is 'descriptive' in that it indicates the nature, function, or type of content in a document, rather than specifying how that data content should be displayed, printed on paper, or otherwise processed.