These are the odds offered which vary from casino to casino. Usually expressed as "Double Odds", 3X, 4X, 5X, 10X, or even as high as 100X.
If you bet $20 on the Pass Line, Don’t Pass, Come, or Don’t Come, you can increase your original bet by the double the amount of your free odds after the dice have been thrown - to wager behind. To wager behind is what a good craps player will do and a criteria of good craps games is how many free odds the casino offers you. As the amount of allowed odds increases, the house advantage decreases considerably.