XML, or Extensible Markup Language, is a flexible text-based language that facilitates the structuring, storing, and transporting of data. It is a markup language much like HTML and was designed to be both human-readable and machine-readable. Unlike HTML, which is used to display data and focuses on how data looks, XML is solely concerned with the data itself. One of the key features of XML is that it is extensible, meaning that it allows users to define their own tags and document structure. This makes it incredibly versatile and adaptable to a wide range of applications, including web development, software configuration, data exchange in business transactions, and more. XML plays a crucial role in many different IT systems and is often used in conjunction with other technologies such as XSLT for data presentation and XPath for data navigation. Its self-descriptive nature, where tags can be named in a way that describes the data they contain, makes it easy to understand and work with. Moreover, XML is platform-independent and can be used across different systems and programs, which is essential for modern internet-based applications and services that require data sharing and interoperability.