He wanted to distinguish the "known knowns" from the "unknown knowns"

Some people evidently had too much time on their hands:

Donald Rumsfeld had to be talked out of editing his own entry on Wikipedia, which he referred to as “Wika-wakka.” He was a Drudge Report reader and used to watch YouTube clips that made fun of his press conference performances.

Good thing there’s not a “Rate My Defense Secretary” site. Rummy totally would have given himself a chili pepper.

Rumsfeld’s Wika-wakaa page, incidentally, has already been updated to include this important news.