What is a markup language?
A markup language is a type of computer language that is primarily used for the processing, definition and presentation of text. Basically, it tries to define to the computer how it should process, define, and show the text.
The language is typically used in a text file and specifies the code for formatting both the layout and style, via the use of tags. These tags, such as <bold>, <underline>, etc. indicate to the browser that the text marked by it should be displayed as such.
A markup language can also be used for transporting and storing data.
HTML, XML, and XHTML are some of the most common and popular examples of a markup language.