So here you have two definitions of a blue moon but the one for a calendar blue moon does not describe the true meaning of a blue moon. Here's why:
Water in its life-sustaining liquid phase exists beyond our own planet, both in our Solar System--and elsewhere. With oceans of water sloshing around on 71% of our own planet's surface, Earth still remains the only planet known to have stable bodies of liquid water. Liquid water is essential for all known life forms on Earth. The existence of water on the surface of Earth is the outcome of its atmospheric pressure and a stable orbit in our Sun;s circumstellar habitable zone. The habitable zone is that Goldilocks region, surrounding a star, where the temperature is not too hot, not too cold, but just right for life sustaining water to exist in its liquid phase. However, the origin of Earth's water still remains unknown.
A New Moon is when the moon takes its monthly promenade and reaches the phase where it comes to rest between the sun and Earth, in this position the moon's dark side is facing us making it seem 'invisible'.