A Horn or craps-11 bet, as it is typically called, is a one-roll wager that on the next roll of the dice their sum will be 2, 3, 11 or 12. If they total anything different (4, 5, 6, 7, 8, 9 or 10), you lose. If 3 or 11 appears, you are paid 15:1.
A round robin (RR) bet allows you to combine multiple parlays into one bet. The more selections you make, the more parlay combinations you will have in your RR. Once you make your selections, an RR will create parlays of all possible combinations between them.