What is global refference in php

$GLOBALS — References all variables available in global scope

<?phpfunction test() {
$foo = "local variable";

echo '$foo in global scope: ' . $GLOBALS["foo"] . "\n";
echo '$foo in current scope: ' . $foo . "\n";
}
$foo = "Example content";test();?>

$foo in global scope: Example content
$foo in current scope: local variable