A Gibbous Moon is the lunar phase that happens mid way between Full Moon, when the side of the Moon facing the Earth is fully illuminated by the Sun, and First or Third Quarter when half of the Moon facing the Earth is illuminated. Between Full and First quarter, this is called the Waxing Gibbous; between Full Moon and Third Quarter, its is called the Waning Gibbous. The progress of the phases is from First Quarter, to Full Moon and then to Third Quarter.