A hand pay is simply when you win a certain amount of money on a slot machine over the amount that is required to be reported for tax purposes, and when you win such a payout or jackpot the casino slot attendant will pay you your winnings in cash on the spot. However, if you are from one of several different countries and you do win a hand pay or a large jackpot then you will not be required to pay any tax on those winnings, for more details checkout the US Gov. Website for more details.