The Arizona Cardinals have placed quarterback Kurt Warner on the Reserve/Retired list. By placing Warner on the list, he won’t count against Arizona's roster limit and his salary is off the books unless he decides to come back. If Warner decides to play again, all he needs to do is notify the league in writing.
This is a formality by the Cardinals, and it remains incredibly unlikely that Warner would even consider returning. If he does, he would be coveted by many fantasy owners and mandate plenty of changes in draft strategy and the quarterback rankings.