Question regarding a Tutorial from jQuery Missing Manual

Question regarding a Tutorial from jQuery Missing Manual

This is with regard to the Quiz tutorial.

The script goes like this,

<script>
var score=0;
var questions = [
 ['How many moons does Earth have?', 1],
 ['How many moons does Saturn have?',31],
 ['How many moons does Venus have?', 0]
];
function askQuestion(question) {
 var answer = prompt(question[0],'');
    if (answer == question[1]) {
        alert('Correct!');
        score++;
    } else {
        alert('Sorry. The correct answer is ' + question[1]);
    }
}
for (var i=0; i<questions.length; i++) {
 askQuestion(questions[i]);
}

</script>

Everything works fine. But I don't understand the part where we define the function  askQuestion.  
i.e.       function askQuestion(question) {
 var answer = prompt(question[0],'');
    if (answer == question[1]) {
        alert('Correct!');
        score++;
    } else {
        alert('Sorry. The correct answer is ' + question[1]);
    }


How is the function able to understand "question" when we haven't defined any variable by that name.
We only defined the array "questions".

Please help me understand this.