X.509: An ITU-T standard for public key infrastructure subsequently adapted by the IETF, as specified in [RFC3280].
X500 DN: A distinguished name (DN), in Teletex form, of an object that is in an address book. An X500 DN can be more limited in the size and number of relative distinguished names (RDNs) than a full DN.
XML: The Extensible Markup Language, as described in [XML1.0].
XML document: A document object that is well formed, as described in [XML], and might be valid. An XML document has a logical structure that is composed of declarations, elements, comments, character references, and processing instructions. It also has a physical structure that is composed of entities, starting with the root, or document, entity.
XML element: An XML structure that typically consists of a start tag, an end tag, and the information between those tags. Elements can have attributes (1) and can contain other elements.
XML namespace: A collection of names that is used to identify elements, types, and attributes in XML documents identified in a URI reference [RFC3986]. A combination of XML namespace and local name allows XML documents to use elements, types, and attributes that have the same names but come from different sources. For more information, see [XMLNS-2ED].
XML namespace prefix: An abbreviated form of an XML namespace, as described in [XML].
XML schema: A description of a type of XML document that is typically expressed in terms of constraints on the structure and content of documents of that type, in addition to the basic syntax constraints that are imposed by XML itself. An XML schema provides a view of a document type at a relatively high level of abstraction.
XML schema definition (XSD): The World Wide Web Consortium (W3C) standard language that is used in defining XML schemas. Schemas are useful for enforcing structure and constraining the types of data that can be used validly within other XML documents. XML schema definition refers to the fully specified and currently recommended standard for use in authoring XML schemas.
XMLHTTPRequest (XHR): A software component that is used by browser-based scripts to transfer data between a web browser and a web server.