Gasless transactions are made possible by a network of Ethereum relayers.

What is a relayer? When you attempt to make a transaction on the Ethereum blockchain, your transaction needs to be processed by the miners in order to get written on the blockchain. These miners are incentivized to process your transaction since they can collect gas fees for their work.

That’s where relayers come in - they relay your transactions to the miners and collect your gas payment for you. They allow you to effectively skip two steps (sending ETH and then broadcasting a transaction) when using MetaMask.

This repo implements a simple version of gasless meta transactions using openzeppelin defender relayers.

Read more on this here https://docs.openzeppelin.com/defender/relay