When there are two Full Moons in a month (which occurs, on average,
every 2.7 years),the second one is called a "Blue Moon".

Black satin with  dusky blue mane and tail,  and wearing nothing but antique blue  roses and vines ... Carousel Unicorn"Blue Moon", is  romantic ,  mystical .  and handcrafted with magic--3, 4, or 6 feet tall--He comes along once in a blue moon!