Gas
On networks such as Ethereum, gas is a measure of the computational work required to process an interaction.
Fee
The final fee can depend on how much gas is used and the price assigned to each unit. Network conditions can influence that cost.
Not every network uses the same model
Each blockchain can have its own fee and resource structure. The term gas is especially associated with Ethereum-compatible networks.
Gas and smart contracts
A more complex interaction can require more resources than a simple one. This is why different operations can consume different amounts of gas.