11 o'clock number is a theatre term for a big, show-stopping song that occurs late in the second act of a two-act musical, in which a major character, often the protagonist, comes to an important realization.
[1] It was so named because in the days when musical performances would start at 8:30 p.m., this song would occur around 11:00 p.m.[2] Among the theatre community, there is some debate as to the characteristics of an 11 o'clock number.
It often signifies a moment of revelation or change of heart of a lead character, although there are exceptions to this.
[4] Broadway producer Jack Viertel defines an 11 o'clock number as "a final star turn".
[5] Other notable 11 o'clock numbers include "Sit Down, You're Rockin' the Boat" from Guys and Dolls,[3] "Memory" from Cats,[6] "Brotherhood of Man" from How to Succeed in Business Without Really Trying,[7] “No Good Deed” from Wicked, "Gimme Gimme" from Thoroughly Modern Millie,[4] "Another National Anthem" from Assassins,[8] "The American Dream" from Miss Saigon, "Goodbye" from Catch Me If You Can, "Revolting Children" from Matilda The Musical, "I'm Here" from The Color Purple,[9] “The Boy Falls from the Sky” from Spider-Man: Turn Off the Dark, “42nd Street” from 42nd Street, “The Power of Love” from Back to the Future: The Musical, and "Always Starting Over" from If/Then.