Fallback

fallback is a function that is called when a function to call does not exist.

For example, call doesNotExist(), this will trigger the fallback function.

Receive Ether

fallback function declared as external payable is commonly used to enable the contract to receive Ether.

There is a slight variation of the fallback called receive.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

contract Fallback {
    string[] public answers = ["receive", "fallback"];

    fallback() external payable{}

    receive() external payable {}
}