XML is a markup language for the structured display of data
XML – short for extensible markup language – is a markup language to present data in a structured way. XML is a file format for all kinds of data: letters, invoices, addresses, stock quotes, whole databases or graphics can be saved with the file type. HTML is primarily for the visual representation of data. With XML alone you can achieve nothing, but it is a standard which is supported by many software packages and programming languages which lets it be displayed on various media, browsers, smartphones and printers. XML lets you display the same data on differently on different media by changing the interface, meaning the data processing program. The underlying data structure can be extended without having an impact on the appearance. Since XML is basically just a text file, it can be easily copied, sent and reproduced. The file content is easy to capture as the structure of the document is normally clear.
XML works across files and systems
XML has a great advantage for the user: XML works in all areas. Even drawings, graphics and databases can be created with XML. Connecting file types to certain programs is even more serious in these formats.
A further advantage is the cross-platform functionality. The character set that is used for XML is limited to the characters that can be read anywhere in the world from any system. Whether on Mac, UNIX, or Palm: the data can be read by any system.
You can find more information on XML on Wikipedia: https://en.wikipedia.org/wiki/XML