n. A person's 10,000th day since birth.
Approaching his tkday — or 10,000th day on Earth — Horne decided he wanted to leave a permanent mark on history, and as a lover of language and devout Countdown fan, he decided that the best way to do that would be to get a new word into the dictionary.
The 10k Day celebration — alternately called "Tkday" or "decimal birthday" — has become the new coming-of-age for Generation Y.
You'll reach your Tkday when you're about 27 years, 3 months and 15 days.
The domain name tkday.com was registered on October 3, 2006.