Rahbari and Buiter believe that Greece leaving the Euro is highly possible, and that the probability has tipped over 50% for it to occur in the next 18 months from this writing in early February, 2012.
The concept of the "Grexit" is important to investors and others trying to predict the impact on the world economy, on Greece itself and the Greek financial crisis, and on financial interactions around the world.
From the Guardian: Greek Impasse Raises Fears of 'Grexit'
However, Rahbari and Buiter might have wanted to Google "Grexit" before declaring this word - turns out that GrexIt is an email service which can be accessed by going to the eponymous Grexit.com website. They bill themselves as a "smart shared folder for your Google Apps email". Not sure if they will enjoy being synonymous with an impending potential financial disaster in Greece and the rest of Europe.
From a linguistic point of view, it is rare to be able to document the "birth" of a new word as clearly as this one. Etymologists - those who make a study of words - should be delirious with joy over this new one, but they will probably be the only ones happy over this development.
While a "Grexit" is still possible after the June elections seem to have reinstated pro-bailout forces, what is more likely is the possibility of one or more bridge loans for Greece to help manage Greece's debt and avoid a full default. Want to learn another word you should know about the Greek financial crisis? Check out What Is The Troika?