Leveraged yield farming is a concept allowing farmers to lever up their yield farming position, meaning to borrow external liquidity and add to their liquidity to yield farm.
In simple terms - you can earn income on your asset and use your LP position to borrow extra liquidity and reinvest these extra funds. Given that your asset APY is higher than your loan APR, you can get a 100-200% boost on your profits. Let's see an example.
At the time of writing, the Stability Fee (APR) of your loan using yvcrvUSDN LP position is 2.9%. But you can earn more than 14% APY on your USDP stablecoin using the same farm (crvUSDN).
So you can invest USDP in crvUSDN and earn the difference, but then you can take a USDP loan again and repeat the process. The caveat is - you can't borrow 100% of your LP position; hence every next loan is smaller in size.
Finally, if you repeat the process 10 times, your expected yearly return will be 45%, is three times higher than the base APY of crvUSDN farm (14%).