The Flash Return Rate (FRR) is a floating rate based on the average of all fixed-rate positions, of all terms, weighted by their respective amount. The FRR updates once every hour and can be found on the market statistics page.
The advantage of using the FRR is that return rates tend to follow the market action. Taking the ETH/USD pair as an example - when the market price goes up, return rates for USD also tend to go up, and the case is similar for ETH return rates when the market price goes down.
By using the FRR, funding providers can provide funding, safely knowing that they will not miss opportunities if the market return rate goes up.