Ok, after re-reading the "waitlist" email from the Asst. Dean of Admissions at UIUC, I realize that I too quickly made the assumption that the meaning of "On Hold" was the equivalent of a Waitlist.
He said, and I quote: "We have placed you in the “HOLD” category of applicants who will be receiving a close second look. When your application is reconsidered, you could be admitted, placed on a waiting list, or denied."
So it turns out this hold business is clearly not a waitlist. So what does this mean? Are there many that fall into the "hold" category?