Those numbers are showing how students who were offered a seat in BSOM's class are withdrawing after choosing other schools. It's of interest to people on the waitlist because (in theory) when enough accepted students decline, the school starts to accept students off of the waitlists. However, schools purposefully accept way more students than they plan to enroll in anticipation of this. I think BSOM is aiming for a class of 130 so basically according to that portal at least 12 more accepted students need to decline before they go to the waitlist.