Funding rates are small payments exchanged between long and short traders on perpetual futures. They keep the futures price close to the spot price. When funding is positive, longs pay shorts. Means the crowd is betting on higher prices.
When it's negative, shorts pay longs. The market is leaning bearish. Earlier this month, every major crypto on Binance went negative funding at the same time. That's rare.
And historically, when the whole market flips negative like that, it tends to mark the point where most of the selling is already done. Not a buy signal on its own, but worth paying attention to.