In the method addEventListener, how does passing a parameter x to anonymous function that implement console.log(x) can return the event?

I don't understand how the console.log(x) works in the situation below. I understand that addEventListener("keydown", function) means when keydown, do the function (here print to console).

However, I really can't grasp how things work when we pass a parameter to an anonymous function(here x) in method addEventListener(), then implementing console.log(x) will print the keydown event to console.

document.addEventListener("keydown", function(x) {
console.log(x); // e.g. KeyboardEvent {isTrusted: true, key: "x", code: "KeyX", location: 0, ctrlKey: false, …}
});

same with (one small notice that with event I can just use function() and it's still working):

document.addEventListener("keydown", function() { //here no need to input `event` as parameter
console.log(event); // e.g. KeyboardEvent {isTrusted: true, key: "x", code: "KeyX", location: 0, ctrlKey: false, …}
});

but

document.addEventListener("keydown", function() { //no parameter
console.log(x); // Uncaught ReferenceError: x is not defined
});

Read more here: https://stackoverflow.com/questions/66279016/in-the-method-addeventlistener-how-does-passing-a-parameter-x-to-anonymous-func