If no team scores a golden goal during the extra time, a penalty shoot-out decides the outcome.
Even though this kind of arrangement is known as sudden death in some other games, and the term sudden death is also informally used when speaking about football, the only official term is "golden goal". The term golden goal was introduced by FIFA along with the rule change because "sudden death" was perceived to have negative connotations.
Due to the unpopularity of the golden goal, from the 2002 season UEFA have introduced a new golden goal rule, the so-called silver goal. In extra time a team leading at half-time or full-time will win but the game will not stop the instant a team scores. This change was decided after 'golden goal' victories led to some ugly behaviour from the losing teams.
The silver goal was first employed in the 2003 UEFA Cup final between Porto and Celtic. A penalty in the first half of extra time gave Porto its 3-2 winning margin.