Refers to a text file that contains information fields (the tags) embedded within the words, sentences and paragraphs. The tags are also text, but are contained within unique start and end symbols; typically the less-than and greater-than characters (< and >), although other symbols have been used.

A Lot of Tagged Text These Days
Most word processing formats and all page layout formats use tagged text to describe how the text is displayed and printed. HTML and XML documents are also tagged text files. The tags in HTML files serve the same purpose as word processing and page layout; they describe the format of the output. The tags in XML files describe the data in the file. See text file, HTML and XML.