What Makes a Word a Word?

Oxford University Press, the supposed authority on the English language has recently been updating the dictionary. Every living language evolves, with slang as well as words falling in or out of favor, and meanings changing. I would think though that instead of regional (or these days, media generated) changes that are as popular as long as a show or fad lasts, the words would have staying power.

But Oxford claims they very much research these words. Their criteria are listed on their site...