eXtensible Messaging and Presence Protocol (XMPP), or Jabber, is a communications Protocol that aims to help connect different kinds of messaging platforms or Middleware. Built on eXtensible Markup Language (XML), this protocol is sometimes called “Jabber,” which is technically a service based on XMPP, and provides an open standard for engineering messaging compatibility.
Source: https://www.techopedia.com/definition/396/extensible-messaging-and-presence-protocol-xmpp