We've had many lively debates on this topic at my board!
From what I recall when I looked into it, as you say, Robert's Rules of Order suggests that adjournment is the orthodox and accepted term for ending a meeting (i.e., the business of the meeting is complete, or if the members move to adjourn despite business not being complete). Something less, like a break, would be a recess. A longer (i.e., overnight) mid-meeting break would be adjourning to a particular date and time (so no new notice would have to be given for the continuation), but "adjournment" also seems like commonly accepted terminology for ending a meeting at many bodies that I looked into.
Then you've got those who want to use the term "terminate" to signify the meeting is over as opposed to being resumed in the future. They use adjournment in the legal sense of the word -- a pause in proceedings -- whereas termination signifies the end of the meeting. I get it, but personally I think the distinction is unnecessary. In a sense, every meeting is adjourned until the next one -- the word recognizes the body will continue on and meet again. I find "terminate" awkward and confusing for those who are used to hearing the time-honoured "meeting adjourned".
At the end of the day, I view the distinction as merely a difference in preference for one convention over the other, without any real governance impacts, except to those of us who take these terms very seriously :-)
Interested to hear if others have arrived at different conclusions...
