XML (eXtensible Markup Language)

XML, short for eXtensible Markup Language, is a markup language that defines a set of rules for encoding documents in a format readable by both humans and machines.

Developed by the World Wide Web Consortium (W3C) and first published as a recommendation in February 1998, XML has from the outset been intended to facilitate the exchange of structured data across the Internet and the purpose of storing and transporting data, rather than for displaying it; it has also served to define other markup languages specific to certain industries or applications, such as RSS for news feeds or XHTML for Web content.

Key features of XML include its extensibility, which allows developers to create their own custom tags; its self-descriptive nature, in that user-defined tags describe the content of the data; and its platform independence, which allows easy transmission of data between different systems. It is also strictly structured, requiring documents to be well-formed to be considered valid, which facilitates analysis and manipulation of data by software and applications.

In the context of SEO, XML is often used to create sitemaps, which help search engines understand the structure of a website and index its pages more effectively.