If you are "under review", it is the same as "continuing review" at other institutions. Basically, the Admissions Committee has found your application acceptable, but upon ranking, your file didn't make the cutoff for the number of offers we have left to issue for that round. Your file is reranked for the next round.
Essentially your chances of getting admitted depend on how many seats are still remaining after an offer deadline has passed. As I tell everyone on interview day, we don't operate like the airlines do and overbook a flight. We play things conservatively because we recognize there are some excellent applicants that we still have in our pool that wind up having later interview spots.
This is at least why we ask anyone to contact us if they have been accepted elsewhere and will not be using their reserved interview slot for us. It allows us to pick up other applicants that could be invited to interview but are not. No shows to interview days block potential applicants from being considered with us, especially if we still have seats open. We continue to interview until May, and depending on our responses to our offers, we might still have a handful of seats left when our interviews are done... but it depends on the responses we get.
