In pari-mutuel betting, when so much money is bet on a horse (usually to show) that the pool is insufficient to pay the holders of winning tickets. The track is required to make up the difference from its own funds.
a mutual pool caused when one horse is so heavily wagered on, that after deductions of state tax and commission, there is not enough money left to pay the legally prescribed minimum on each winning bet.
In pari-mutuel wagering, when after the take is extracted, there is not enough money left to pay winning patrons the minimum pay-out. The track must then make up the difference