A gentleman's agreement (which isn't allowed in some casinos) where the players (usually two or three) agree to draw each remaining card to come in two different occasions instead of just once after all parties have gone all-in (two flops, turns and river for example for a total of 10 community cards in 2 sets of 5). You may run twice the flop, turn and river or just the turn and river or only the river. Cards are usually not run retroactively unless the players expressly request so (which is rare). The winner of one "run" gets half the pot while the winner of the second "run" gets the other half. Running it twice is done to minimise bad beats and remove variance (which works well if the hands are equally likely to win the hand but not so well if one is dominated over the other). Running it twice is a form of insurance.