Extensible Markup Language (XML) is a markup language designed for encoding documents in a format that is both human-readable and machine-readable. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all free open standards. XML is widely used to represent arbitrary data structures, particularly in web services, configuration files, and data interchange between applications. Its self-describing nature, through the use of tags, allows for flexible and adaptable data representation. XML documents can be validated against schemas (like DTD or XSD) to ensure data integrity and consistency. The hierarchical structure of XML makes it suitable for representing complex relationships between data elements. It is a foundational technology for many other standards and technologies.