The word markup is a noun. Markup means (1) 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) the amount added to the cost to determine the asking price.
The following articles and web pages elaborate on the word markup.
This is a free service that checks web documents in formats like HTML and XHTML for conformance to W3C recommendations and other standards. Can be searched by URL, File Upload, or Direct Input.