Glossary
What is gas in crypto?
In one sentence
Gas is the fee you pay to have a transaction processed on Ethereum and similar networks. It rises when the network is busy.
Every operation on Ethereum consumes computing resources, and gas is how that consumption is priced. A simple transfer uses little; a complex smart contract interaction uses much more.
Your total fee is roughly the amount of gas used multiplied by the gas price you are willing to pay. Because block space is limited and demand varies, the price is an auction: when the network is congested, users bid higher to be included sooner, and fees can rise sharply within minutes.
Two practical consequences for newcomers. First, a small transaction can cost more in gas than it is worth — moving $20 during congestion may be uneconomic. Second, a failed transaction still consumes gas, because the network did the work before the failure. You can pay a fee and get nothing.
Fees vary by time of day and by network; layer-two networks exist largely to make this cheaper.
For example
If a swap fails because of slippage, you still pay the gas. The work was done even though the outcome was rejected.