Not really United specific, but:
They're almost always given together and "Terms&Conditions" (or T&C) is practically one word in practical (i.e. FlyerTalk) usage.

That said, maybe one way to think of it is terms of an offer or promotion are the basic outline of what's being offered (say, fly 10 segments and get a back rub and 3 drink coupons) while the conditions are the limitations or restrictions on what qualifies and what is offered (the flights must be on W or V fares only, and take place before September 15th, the back rub and drink coupons are only valid in IAD terminal G on Tuesdays in October, and you must register before the flights to qualify).
Note: this is not a real promotion

I suspect if one called MP to inquire about a promotion the answer would be exactly the same whether the question was phrased "What are the terms of this offer?" or "What are the conditions of this offer?"