Consignors carry a running balance with the barn. If they owe money (for example a prior overpayment or an unpaid charge), that debt is applied here and reduces what they're paid. If the barn owes them a credit, it's applied here and increases the payout. This is how an old balance gets squared up on the next settlement instead of lingering.
A credit increases net payable; a debt decreases it. The figure here is whatever portion of the consignor's running balance was pulled into this settlement.