What is the 0.3% fee for Uniswap?

Can you clarify what the 0.3% fee for Uniswap entails? Is this a transaction fee that users need to pay when they swap tokens on the platform? Or is it a fee charged by Uniswap itself for using its services? Additionally, is this fee applied to both sides of the swap, or is it just charged to one party? Lastly, is there any way to reduce or avoid this fee, perhaps through staking or holding a certain amount of UNI tokens?