The supplemental draft is held usually in the summer, it is mostly for college players who assumed that they would be back in school, but are ruled to be academically, or otherwise ineligible by the NCAA.
Last year it was Ahmad Brooks, a Linebacker from Virginia.
Cinnicinati took him in the third round, so they forfiet their third round pick in this upcoming draft, and all the other teams move up one.
The way the supplemental draft works is that teams pick in the same order as the regular draft. Teams can either pick a player or pass their pick. If a team uses their pick, then they get the player and lose the corresponding pick in the next years draft.
So last year every team passed through the first two rounds, and then Cincy picked Brooks in the thrid round, which is why they do not have a thrid round pick in this draft.