I mean deferral means they are still looking to consider your application if your profile happens to fit a very specific niche they need to fill during RDs (eg. you’re a first-gen latino male etc.). Don’t worry too much about it though! but I highly recommend for you to email the admissions office to confirm that you are still willing to go through with your application and that BU is still your top choice - only if it really is your top choice though.