Funding payments are explained in full under Funding Rate (Perpetual Futures), which covers how the rate is calculated and what it signals about the market. This page gives a short definition and explains how the payment differs from the rate.
A perpetual futures contract has no expiry date, so unlike an ordinary futures contract it never settles at the spot price. To stop its price drifting too far from the underlying asset, exchanges make traders on one side pay those on the other at regular intervals, often every eight hours. When the perpetual trades above the spot price, the funding rate is positive and traders holding long positions pay those holding short positions; when it trades below, shorts pay longs. The exchange usually acts only as the go-between and does not keep the payment.
The funding rate is the percentage set for each interval, while the funding payment is the actual amount a trader pays or receives, found by multiplying the rate by the size of the position. A trader holding a 10,000-dollar long position when the rate is 0.01% would pay 1 dollar for that interval. Payments add up over time and can make a leveraged position costly to hold, so traders watch them closely alongside initial margin and the risk of forced liquidation.