The supermoon of December is the only full moon supermoon of the year and it will appear on December 3rd. A supermoon happens when the moon is full or new when it’s at it’s closest point to the Earth in its monthly orbit.
The term was coined by astrologer Richard Noelle and before that it was just referred to as perigree full moon or perigree new moon.
According to Spaceweather…
Perigee just means “near Earth.” The moon is full, or opposite Earth from the sun, once each month. It’s new, or more or less between the Earth and sun, once each month. And, every month, as the moon orbits Earth, it comes closest to Earth. That point is called perigee. The moon always swings farthest away once each month; that point is called apogee.