1. [n]  detailed stylistic instructions for typesetting something that is to be printed; manual markup is usually written on the copy (e.g. underlining words that are to be set in italics)
2. [n]  the amount added to the cost to determine the asking price

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

For example, the source of this dictionary is marked up by enclosing cross-references in curly braces which are significant to the World-Wide Web server software.