The golden rule is an abbreviated reference to the statement that the sum of all morality is "Do unto others as you have them do unto you." Although it is attributed to Jesus, various forms of the rule have existed throughout history and long predated Jesus.
The Golden rule is usually refered to as the 'greatest message of Jesus', however it can be pointed out that the Golden Rule is worded extremely poorly. What if you are a masochist? Should you go out and hurt people because you enjoy pain yourself? This can be an extremely dangerous thing to say, especially to a die hard Christian with persecution syndrome.