Party Passes may be used in place of Gems to pay for Vegas World Charm Parties. Passes are most often given as gifts but can also be collected through Loyalty Rewards, the Treasure Box, and games like Sea of Riches.
When any number of Party Passes are added to your account, either as a gift or a prize, you'll see your Party Pass balance go up to match. Your balance is always displayed at the top of the Party display.
Note: Vegas World always collects Party Passes before it'll collect Gems to pay for a Charm Party. That means if you are given Party Passes while you are in a Charm Party, the game will take those passes to pay for that same party, even if you had agreed to pay Gems when you entered.