In my mind there is a difference... although VERY slight it is there.
Limits is what I don't enjoy... hard limits what I won't participate in. Guess the word "limit" is focused more on the play aspect of it in a way for me. Such as a hard limit for me is tickling... won't do it,
Terms are more of a "what will/won't work" in the relationship. Such as, I have to be home by a certain time each day for the kids... there fore I would NEVER accept a task that would prevent that from happening. That is a term I would place up front on the relationship, and make sure the Dom understood first and foremost before moving ahead with any relationship.
You are correct, the phrase is interchangeable to me in many ways... but to me a "limit" may be pushed (and in some ways those are expected to be pushed a tiny bit) but a "term" is a firm fact that i, as the submissive, felt it was necessary establish in the relationship, therefore taking any "control" aspect away from the Dom on that one issue. Not that I wouldn't negotiate, if it was appropriate, but it would probably be limited at best.
So now that I have mudded that even further....
Thanks for all the great comments... keep 'em coming!