What Does Extensible Messaging and Presence Protocol (XMPP) Mean?
Extensible Messaging and Presence Protocol (XMPP) 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.
Techopedia Explains Extensible Messaging and Presence Protocol (XMPP)
XMPP was built to provide full support for cross-platform messaging so that one proprietary system's users could talk to another's. But some of the drawbacks of this protocol, including more vulnerability to certain kinds of spam, and limitation of platform capacity, led to some major tech companies, including Google, limiting some of their support for XMPP. The controversy between fully opening up messaging protocol and keeping it proprietary has led to talk about the concept of "federation" — the idea that messaging should become more open. In the absence of one universal standard, it seems that companies are considering less compatibility in messaging, as part of broader engineering for their messaging systems.