In blockchain networks, a gas fee refers to the cost associated with executing and validating transactions or smart contracts. It is primarily associated with networks that utilize the Ethereum blockchain, but similar concepts exist in other blockchain ecosystems as well.

Gas fees are paid in the native cryptocurrency of the blockchain network (such as Ether in Ethereum) and are determined by the complexity of the transaction or smart contract, measured in terms of the computational steps or operations it requires. Each operation has a predefined gas cost assigned to it. Additionally, the gas fee can be influenced by network congestion. During periods of high demand, gas fees tend to increase as users compete for limited block space.

It's important to consider gas fees when interacting with blockchain networks, as they can vary greatly depending on network conditions. Users can set their own gas price (the amount of cryptocurrency they are willing to pay per unit of gas) to prioritize their transactions accordingly.