Taken from the saying "It ain't over until the fat lady sings," commonly attributed to ex-Yankee ballplayer Yogi Berra.

Presumably, the "fat lady" in question is a stereotyped opera singer, replete in Wagnerian Rhinemaden garb. Ironically enough, the "fat lady" was usually singing the United States National Anthem, the traditional way to START a baseball game.
Sure, we're behind by 300 points. But it ain't over until the fat lady sings.
by Packy April 11, 2004
The Games is over
Kate Smith (the fat lady) singing at the end of the Flyers game.
by kioran June 14, 2012
To show up to work late, hungover and/or still drunk. A term used by English speaking ex-pats living in Venice, Italy. The term is rumoured to have originated from being stuck behind a fat lady on crutches in the narrow streets of Venice, it was rumoured to have been originally an excuse for being late to work, the current definition has grown to incorporate being both late and generally unfit to work.
Mel was so Fat Ladied this morning, she was late and looked like she hadn't slept last night!
by Italian Nick June 2, 2011
My fat ladies beat your treys! Muahahahahahahah!
by rhaps0dy August 4, 2004
Meaning that nothing is gonna end till the very last point and till the very last options are gone.
I failed on my spanish test, but it aint over till the fat lady sings!!
by keru smith November 20, 2013
In opera, audiences would start to leave in between acts thinking it was over. Many operas supposedly announced the end when a blonde women with long braids and a Viking helmet with horns would sing.
by ncncsr11 June 8, 2020