The whole nine yards means absolutely everything that goes with it. Went the whole nine yards, the whole nine yards of it, give them the whole nine yards.
The origin is genuinely unknown and is one of the most argued-over questions in English etymology, with confident explanations about ammunition belts and cloth all failing on the dates. It is American and appears in print in the 1950s.
1phrasethe whole nine yardsAbsolutely everything that goes with it.
“They went the whole nine yards for the wedding, with flowers, a band and fireworks.”
the whole nine yards is an everything.
Also accepted in games: whole nine yards
Of unknown origin despite many confident theories; it appears in American print in the 1950s.
Dave Wilton summarises the findings of Bonnie Taylor-Blake and others:
Etymology from Wiktionary, CC BY-SA
Practised in Idioms