XML
noun
Extensible Markup Language. A flexible way to create common information formats and share both the format and the data on the World Wide Web, intranets, and elsewhere.

XML

What is XML?

• XML stands for EXtensible Markup Language
• XML is a markup language much like HTML
• XML was designed to describe data
• XML tags are not predefined. You must define your own tags
• XML uses a Document Type Definition (DTD) or an XML Schema to describe the data
• XML with a DTD or XML Schema is designed to be self-descriptive
• XML is a W3C Recommendation

The Main Difference Between XML and HTML

XML was designed to carry data. XML is not a replacement for HTML.

XML and HTML were designed with different goals:

• XML was designed to describe data and to focus on what data is.
• HTML was designed to display data and to focus on how data looks.

HTML is about displaying information, while XML is about describing information. With XML, your data is stored outside your HTML.

Source: w3schools.com