markup

In computerised document preparation, a method of adding information to the text to indicate the logical components of a document, instructions for layout of the text on the page or other information which can be interpreted by some automatic system.

For example, HTML (Hypertext Markup Language) adds tags to the text to indicate the appearance and behaviour it should have when displayed by a web browser. E.g.:

 This is bold text.

 ___1___

Other examples of markup languages are troff, SGML (on which HTML was based) and XML.