411 REFERENCE · Wiktionary
11 o'clock number
Reference material by Wiktionary contributors. This retains its source identity and is not 411 news reporting.
English
Etymology
So called because, in the days when musical performances began at 8:30 p.m., such a song would occur around 11 p.m.
Noun
en theatre A showstopping song that occurs late in the second act of a two-act musical, often signifying a moment of revelation or change of heart of a lead character.
See also
en 11th hour