Shorter version than the Wikipedia link.
Jabber is another form of messaging.
It has been in Messages since it's beginning at version 7
It was in iChat before that from iChat 3 until iChat 6 (which is the one where iChat ended and Messages began)
Unlike AIM (now defunct since December 2017) and Yahoo (was ended and then rewritten) which had central Servers like iMessages has, Jabber or XMPP has lots of servers that can then pass messages to users linked to that server.
Google run a Jabber server.
In High Sierra you have to add it in System Preferences > Internet Account > Other > Messages account.
You then add in your Google ID, your password and set the Server to google.com and the port to 5223 and use SSL
7:54 pm Monday; April 23, 2018
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