what does that mean name="array[is]" PHP code example

Example 1: php array

<?php
$array = array(
    "foo" => "bar",
    42    => 24,
    "multi" => array(
         "dimensional" => array(
             "array" => "foo"
         )
    )
);

var_dump($array["foo"]);
var_dump($array[42]);
var_dump($array["multi"]["dimensional"]["array"]);
?>

Example 2: php define variables from array associative

<?php
	$array = [
		'key1' => 'foo',
  		'key2' => 'bar',
	];
	extract($array);
	
	echo $key1; //print foo
	echo $key2; //print bar
?>