i want to know the meaning of this idiomatic expression "it is not over untill the fat lady sings".
It ain't over 'til the fat lady sings
It ain't over 'til the fat lady sings is a proverb, essentially meaning that one shouldn't assume the outcome of some activity (frequently a sports game) until it has actually finished.
It is a common expression in the theatre of North American sports. Attributed to writer/broadcaster Dan Cook, his original line was "The opera ain't over until the fat lady sings." This occurred in April 1978, when he coined the phrase after the first basketball game between the San Antonio Spurs and the Washington Bullets (WWizards) during the 1977-78 National Basketball Association playoffs, to illustrate that while the Spurs had won once, the series was not over yet. This refers to the impression that at the end of every opera an aria is sung by a woman dressed like a valkyrie.
As a possible alternate origin for the term, there exists an old saying in the Southern United States stating that "Church ain't over until the fat lady sings." This form of the line was apparently well known in the South for years, appearing in a booklet in 1976 entitled Southern Words and Sayings.
This saying is also common in Australia, often used in conjunction with games in the National Rugby League or Australian Football League. It usually means that the games not over and either team could still win until "The Fat Lady Sings." This literally refers to the final hooter at the end of the match.