We haven’t seen a Full Moon like this one in over 27 years, and we won’t see another one until the 22nd century!
In any given calendar year, there are typically 12 Full Moons — one occurring in each month. Every once in awhile, though, due to the exact timing of when the Full Moons occur, we get an extra one. That means we have a total of 13 Full Moons for the year, one during each of 11 months, and one month with two.
Since we only have 12 popular names for the Full Moons, the extra one goes nameless. Thus we call it a Blue Moon.