Etymology

The origin is unknown, but many theories exist.
The earliest known print appearance in these senses is in an article by Stephen Trumbell in the 1964-04-25 Tuscon Daily Citizen, titled “Talking Hip in the Space Age” and discussing NASA jargon: “‘Give ’em the whole nine yards’ means an item-by-item report on any project.”
The synonymous variant “all nine yards” appeared in a letter from Gale F. Linster to the editor of the 1962-12 Car Life.
There is a supposition that "The whole nine yards" refers to the length of the ammunition belts of the guns on WWII bombers- 9 yards. "Give em the whole nine yards" would then mean give them everything you've got.

Noun

1. All the way; with everything done completely or thoroughly.

   They really went the whole nine yards with this party.

2. And everything. Often used, like etc., to finish out a list.

   They put up balloons, baked a cake, sent out invitations—the whole nine yards.

   They have books, CDs, cassettes, DVDs, the whole nine yards.