here is what i think:
interviewed but 'still under review' = 'on hold' = you were not in our first round of acceptances but we are still considering you for the second, third etc rounds depending on how many of our first choices send in their deposits. The class isn't full yet. chances of you getting in could still be moderate to good.
waitlist = alternate = we have gotten all our deposits, our class is officially full. but if enough people drop out later you might get a spot. chances of you getting in are moderate to slim (probably closer to slim).