eXtensible Markup Language
eXtensible Markup Language (XML) is a markup language for presentation of hierarchically structured data in the form of text data. XML is used especially for the exchange of data between IT systems, specifically via the Internet.
The XML specification released by the World Wide Web Consortium (W3C) defines a metalanguage which serves as a foundation on which the structural and content-related limitations of application-specific languages are based. These limitations are expressed using schema definition languages such as DTD or XML schema. Examples of XML languages are SOAP, XMLA and XBRL.
XML is aided by the fact that an XML document consists exclusively of text characters and is visually readable. This makes it much simpler for IT systems to comprehend and edit XML documents being used between IT systems.
Source: information from Wikipedia