Concentrated Liquidity is what UniSwap V3 is bringing to the table.
Previously, you provided liquidity in pairs from the interval 0 to infinity, but since yields on liquidity are accrued via transaction fees, a lot of liquidity outside a coin's typical price range went untouched.
V3 allows you to provide liquidity at a specific price range. It's an incentive for users to poke positions as prices move outside of their range where transactions are happening and thus yields on transaction fees are accrued. It's a more efficient use of capital.
Leveraged yield farming becomes obsolete with UniSwap v3 because positions are implicitly leveraged. The tighter range that you provide liquidity, the tighter leverage on your liquidity. In other words, it's cheaper to get the same yields in a tight spread than it is in a 0 to infinity spread, because your liquidity will be used first in the price range. You can provide less liquidity for the same yields. If you're earning no yields when prices move outside of your range, you can poke positions into the range to tighten leverage.