Extensible Markup Language (XML)
Definition - What does Extensible Markup Language (XML) mean?
Extensible Markup Language (XML) is a universal format maintained by the W3C used for representation and transfer of structured data on the web or between different applications.
The language uses a structured representation by allowing user to create custom defined tags according to XML Document Type Definition (DTD) standards. The structure of XML document can be represented in the form of a tree known as Document Object Model (DOM).
Techopedia explains Extensible Markup Language (XML)
XML is designed to describe data but is not concerned with the data's visualization. The tags created in XML are self explanatory and the user is free to define their own tags - hence the extensible.
XML support is provided by many programming language platforms to create and process XML data. Simplicity, portability, platform independence, usability are some of the key features that have resulted in the increasing popularity of the use of XML based standards.
XML has been the main source of motivation for development of Service Oriented Architecture (SOA) platforms such as Web Services that are not tied to any particular language and collaborate effectively in heterogeneous environments. RSS, Atom, SOAP, XHTML are some of the standards influenced by XML.