This specialized markup language is not used for programming, but for storing structured text data. It specifies the form in which data will be stored, loaded and processed.
XML can be used to store practically anything that can be represented as text.
Use
XML is most often used to exchange data between different programs: warehouse systems and accounting systems, a content management system and an online shop, and so on. Data is exported from one system into XML and loaded by the other system. XML is, figuratively speaking, a bridge between different applications.
XML is very similar to HTML. The only difference between the two is that HTML is used to define the content of a web page, whereas XML is used to define data structures.