What does "the whole nine yards" mean — and why is it funny?

informal, American

Meaning

Everything; the full extent of something, with nothing left out.

Where it comes from

The true source is famously unknown — guesses range from fabric lengths to ammunition belts — and that mystery has become part of the phrase's charm.

Why it is funny

It is quietly funny because it sounds precise but means nothing measurable. 'Nine yards' has the confidence of a real figure, yet nobody can say nine yards of what. The phrase is a number cosplaying as information.

Used in a sentence

"They decorated for the party — balloons, banners, a band, the whole nine yards."