Extensible Markup Language (XML) is a structured language, actually a “meta language” that was published as a W3C Recommendation in 1998. It’s called a meta language because it’s used to describe other languages, the elements they can contain and how those elements can be used. These standardized specifications for specific types of information make them, and the information that they describe, very portable.

Organizations like OASIS and W3C have developed many standards based on XML of particular importance to information security on the Internet, including SAML and WS-Security.