Calling vs invoking a function

The difference is semantic and subtle. When you call a function, you are directly telling it to run. When you invoke a function, you are letting something run it.

There is one way to call a function:

myFunction()

Here, you are invoking the function (letting it run) by calling it directly.

There are many ways to invoke a function (given throughout different comments and answers). Here's one example:

function invoker(functionName) {
  functionName() 
}

invoker(myFunction)

Here, by calling invoker, you are invoking myFunction, which is being called indirectly.

Your reference text:

It is common to use the term "call a function" instead of "invoke a function" ... In this tutorial, we will use invoke, because a JavaScript function can be invoked without being called.

Now let me rephrase it:

It is common to use the term "call a function" instead of "invoke a function" ... In this tutorial, we will use the term invoke instead of call, because a JavaScript function can be invoked indirectly like fn.call() and fn.apply() without being called directly like fn().

So, when I do fn(), it's invoked directly and when I do it like fn.call(), it's invoked indirectly but in both cases, the function is being invoked. Otherwise, I see no difference here and I can also say that I can call a function in many ways, for example:

fn(); // I'm calling it
fn.call(); // I'm calling it
fn.apply(); // I'm calling it

So, the difference is semantic but both are interchangeable, IMO. BTW, I wrote a comment above, under the question and I would like to put it here, which is:

IMO, that's a misleading statement. Maybe there are some indication of call/apply or something else but it's totally confusing.