Fallback Function

The fallback function is a function that is called when a contract receives a message that either does not specify a function to call or specifies a function to call that does not exist. The fallback function is defined using the fallback keyword in Solidity.

In older versions of Solidity (prior to version 0.6.0), the fallback function was automatically called when a contract received ether without data. In the current version of Solidity, a separate function called receive is used to handle ether transfers.

Here is an example of a fallback function in Solidity:

contract MyContract {
    // Fallback function
    fallback() external {
        // Do something if no function is called or function does not exist
    }
}

It's important to note that fallback functions are no longer the recommended way to receive ether transfers. Instead, the receive function should be used for this purpose.

Contracts — Solidity 0.8.19 documentation