On February 3, 1959, a small plane holding Buddy Holly, Ritchie Valens, and J.P. Richardson (The Big Bopper) crashed shortly after take-off in Iowa. Americans who paid attention to popular music circa 1971 know this as "the day the music died." That allusion comes from the song "American Pie," which has been analyzed and annotated for more than three decades.
But rather than playing that game, we're crossing genres and checking out another musical metaphor: "It ain't over 'til the fat lady sings."
The fat lady refers to the opera singer whose body is as full as her voice. It is not uncommon for the heroine to sing during the final act of an opera; as starstruck members of the audience know, the curtain doesn't come down until the lady stops singing. The jocular "it ain't over 'til the fat lady sings" is used everywhere from the sports arena to smoke-filled backrooms to indicate action is still possible.
So what's the link between "the day the music died" and a singer heralding the end of the show? Not much. Although both phrases first appeared in print during the 1970s, "the day the music died" traces to songwriter Don McLean (who based it on a Buddy Holly phrase), while the author of "the fat lady singing" remains unknown.