XML

Extensible Markup Language
Extensible Markup Language (XML) is a markup language used to describe data in a document. Similar to HTML, it uses tags (markup symbols) to describe the contents of the data. This is a very flexible markup language that is considered self-describing.

Unlike HTML, XML tags do not necessarily need to be predefined by the language to be valid. Sometimes XML is referred to as a meta language. Any tag can be created to fit the needs of the data being described. Compared to HTML, Which is about syntactic markup of information specifically for content on websites, XML has more broader applications including storing, structuring or transferring data from a database, for example.

XML is a derivative of Standard Generalized Markup Language (SGML). Increasingly, XML is used as a means to transfer data between servers or to a client side application (web browser). The loose structure of the language allows its writers to define the data in accordance to their own specific needs. This prevents programmers from being restricted by the language.