What does & do?

[whoisKeel]

i got this code from php.net to sort multi arrays by key

function tksort(&$array)
  {
  ksort($array);
  foreach(array_keys($array) as $k)
   {
   if(gettype($array[$k])=="array")
     {
     tksort($array[$k]);
     }
   }
  }

What is the &$array part for? it doesn't work without the &, just wondering what it does?

[LordShryku]

It's a reference.