eXtensible Markup Language (XML) is a generic markup language specified by the W3C. The IT industry uses many languages based on XML as data-description languages.
XML tags resemble HTML tags, but XML is much more flexible because it lets users define their own tags. In this way XML acts like a meta-language, viz. a language used for defining other languages, such as RSS. Moreover, HTML is a presentation language, whereas XML is a data-description language. This means that XML has far broader applications than just the Web. For example, Web services can use XML to exchange requests and responses.