A blue moon is when there are TWO (2) full moons in the same month. This event occurs about every three (3) years. The next blue moon won't be until January 2018.
And just so you know, a blue moon is not typically "blue" in color.
So for all you sky watchers out there, let me know if you had a chance to see our blue moon this Friday.... :)
Information gathered from http://www.cnn.com/ author Jareen Imam