A network fee is the fee paid to the miners of the network you are using for your cryptocurrency transaction. This fee is also known as a gas fee.
Every transaction on the blockchain requires a network fee. This is because miners use their own computers to verify and process transactions instead of relying on a central authority.
In return, miners are compensated through network fees. Network fees also incentivizes miners to protect the network from malicious users.
These fees are nonrefundable, even if your transaction fails. Miners still have to use their resources to determine that your transaction failed.
Th Ethereum blockchain pays miners in Ether (ETH), and is called gwei for network fees. But on the Polygon network, the network fees are paid in MATIC.
The network fee you pay will vary according to the network you use.
Uniswap does not receive payment from network fees.