"It ain't over till (or until) the fat lady sings"
is a colloquialism which is often used as a proverb. It means that one should not presume to know the outcome of an event which is still in progress. More specifically, the phrase is used when a situation is (or appears to be) nearing its conclusion. It cautions against assuming that the current state of an event is irreversible and clearly determines how or when the event will end. The phrase is most commonly used in association with organized competitions, particularly sports.
The phrase is generally understood to be a reference to opera sopranos, who were typically heavyset.The imagery of Wagner's opera cycle Der Ring des Nibelungen and its last part, Götterdämmerung, is typically used in depictions accompanying uses of the phrase. The "fat lady" is thus the valkyrie Brünnhilde, who was traditionally presented as a very buxom lady. Her farewell scene lasts almost twenty minutes and leads directly to the finale of the whole Ring Cycle.
