Full information can be found in the PHP Manual
string date ( string $format [, int $timestamp = time() ] )
This parameter determines what is returned by the functon. For example…
date('Y-m-d H:i:s') ⇒ 2013-06-19 09:32:07date('jS M y') ⇒ 19th Jun 13date('Y') ⇒ 2013date('F') ⇒ June
The optional $timestamp parameter is an integer Unix timestamp that defaults to the current local time if a timestamp is not given. In other words, it defaults to the value of time().