Oxford University Press, who edits and publishes the Oxford English Dictionary (the source of all words English) and the New Oxford American Dictionary, has announced its "word of the year" for 2009:

unfriend – verb – To remove someone as a ‘friend’ on a social networking site such as Facebook.

As in, “I decided to unfriend my roommate on Facebook after we had a fight.”

“It has both currency and potential longevity,” notes Christine Lindberg, Senior Lexicographer for Oxford’s US dictionary program. “In the online social networking context, its meaning is understood, so its adoption as a modern verb form makes this an interesting choice for Word of the Year. Most “un-” prefixed words are adjectives (unacceptable, unpleasant), and there are certainly some familiar “un-” verbs (uncap, unpack), but “unfriend” is different from the norm. It assumes a verb sense of “friend” that is really not used (at least not since maybe the 17th century!).

Follow the link to see what other words were considered for the 2009 edition of the New Oxford American Dictionary ("tramp stamp", "death panel", "teabagger", "birther", etc.)