This Weekend’s Moon Event Won’t Happen Again Until 2028
As a result, every two to three years, we experience a 13th moon in the calendar year rather than a single full moon every month. This is called a “blue” moon, because unlike our regular moons, which are all called things like the “flower”, “blood”, and “wolf” moons, they aren’t named.
Article source: https://www.huffingtonpost.co.uk/entry/may-blue-moon-uk_uk_6a194b1ee4b0ea2d03ce317a