That's the New Oxford American Dictionary's 2009 Word of the Year. It means to remove someone as a friend on a social networking Web site such as Facebook.
Each year Oxford University Press tracks how the English language is changing and chooses a word that best reflects the mood of the year.
Oxford lexicographer Christine Lindberg says unfriend has "real lex appeal."
Finalists for 2009 also included netbook, which is a small laptop, and sexting, which is sending sexually explicit texts and pictures by cell phone.