A few of my friends got "hold for interview" letters last year from Penn State. Basically my advisor said that they can only choose, for example, 10 applications a week for interviews from the number they receive that week. So, those who they think should still be interviewed go in the "hold for interview" catagory. If space comes up they then receive interviews. I believe one friend was accepted after finally being interviewed. Two of my other friends who got interviews right away didn't get in, and the other who had the "hold for interview" I don't think ever got one.