Gas is the cost to perform transactions on the Ethereum blockchain. Many types of protocols on the Ethereum network require the use of gas in order for transactions to be performed on the blockchain. For example, decentralised apps (dapps), non-fungible tokens (NFTs), and transfers of funds all require the use of gas.
The price of gas depends on the level of congestion on the Ethereum network while the transaction is processing and the type of transaction an individual is attempting to complete. The more that users are trying to complete transactions at the same time, the higher the cost of gas.
Learn more about Ethereum gas.