Php foreach- Why it doesn't override the array value while iterating?

I have a doubt in php foreach iteration.

Please look my below code.

CODE :

   $arr=array(1,2,3);

    echo '$arr value : '. $arr;

    echo '<br>';

    foreach($arr as $arr){
        echo $arr.'<br>';
    }
    echo '$arr value : '. $arr;

OUTPUT :

$arr value : Array
1
2
3
$arr value : 3

While iterating array i used same array name to value key foreach($arr as $arr) but it works fine. How it is working?.

Why it doesn't override the array value while iterating?

I want to know how foreach iteration is working.

Please Help me!

Thanks in advance Logan