Over in the jdev chatroom just now, someone asked about the distinction between the terms "Jabber" and "XMPP". I knew I had posted a message about it once on one of the jabber.org mailing lists, but it took me a while to track down the message, so I figured I'd repeat the gist here for easier future reference:
The term "Jabber" is, unfortunately, ambiguous. In 1998, Jeremie Miller invented something he called Jabber, and he released it as an open-source project on January 4, 1999. Pretty soon there were many Jabber-related open-source projects, in March 2000 a company called Jabber.com was formed, etc. Over time we have striven to disambiguate the term, thus Jeremie's server was renamed "jabberd" instead of "the Jabber server", we came up with the term "XMPP" instead of "the Jabber protocol", we formed the Jabber Software Foundation to manage the protocols, etc. I think that if "Jabber" means anything as a standalone noun, it refers to the whole ecosystem of protocols, open-source projects, products, companies, server deployments (etc.) that use the underlying XML streams technology invented by Jeremie. However, I never use "Jabber" as a standalone noun, only as an adjective -- see the third section of the usage guidelines -- thus "Jabber community", "Jabber technologies", etc. (but not "Jabber" on its own).
Ther term "XMPP" refers to the core XML streaming protocols contributed by the Jabber Software Foundation to the Internet Standards Process and subsequently published as RFCs 3920 and 3921.
Most XMPP extensions are defined in documents still called (for historical reasons) "Jabber Enhancement Proposals" or JEPs, but in my opinion it is inaccurate to say that "Jabber" = XMPP + JEPs, since there really is no one thing called "Jabber".