XML, or Extensible Markup Language, is a language used for storing and transporting data. It uses tags to define elements of a document, making it a versatile and flexible format for a variety of applications. XML is widely used in web development, particularly in the creation of web services and APIs. It is also used in many desktop and mobile applications for data storage and exchange. XML can be used for a wide range of applications, including web services, data exchange, and document management.