Gas fees are payments required to have a transaction processed or a smart contract executed on certain blockchains, most notably Ethereum. The term reflects the idea that performing computation on the network consumes resources, similar to how a car consumes fuel to travel a distance.
Gas fees fluctuate based on how busy the network is at any given moment. When many people are trying to transact at once, fees rise because users effectively compete by offering higher payments to have their transaction processed sooner. During quieter periods, fees drop significantly.
Different blockchains handle this differently. Some, like Ethereum, have historically experienced highly variable gas fees during busy periods, while newer or alternative networks are often designed specifically to keep fees low and predictable, which is part of why many users have moved certain activities to scaling solutions or alternative chains.