A network cost is the fee paid to the miners of the network you are using for your cryptocurrency transaction.
This cost is also known as a gas fee.
Every transaction on the blockchain requires a network cost. 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. The Ethereum blockchain pays miners in Ether (ETH), and is called gwei.
However, on the Polygon network, the network costs are paid in MATIC. The network cost you pay will vary according to the network you use. Uniswap does not receive payment from network costs.
Network costs are determined by supply and demand of miners.
When there is a lot of traffic on a network (high volume of transactions), the network cost is higher. When there is low traffic on the network (low volume of transactions) the network cost is lower.