Blue Moon Dates
The Blue Moon is so called "blue" when there is a second moon in a particular month. That second moon has a blue-ish tint to its colour as seen from Earth. From the table above of Blue Moon dates you can see that they are indeed a rarity. The previous Blue Moon was on August 31, 2012. The next Blue Moon is on July 31, 2015. Not all Blue Moons are Full Moons.
Monthly Moon Phases and Dates (for Greece and Cyprus)
Blue Moon 2012 by NASA Goddard Photo and Video, on Flickr taken on August 31, 2012. There is not another Blue Moon until July 31, 2015