The Esbats, or Wiccan lunar holy days, celebrate the moon's passage around the Earth. The Esbats offer Wiccans a chance to regularly put aside time to step away from the ordinary world and dedicate time to spiritual reflection or magical work. The approach to the holy days isn't all-inclusive. For each phase of the moon, some groups have particular rituals, and the Esbats can be celebrated by individuals or covens.
Some Wiccans celebrate an Esbat on the:
Full Moon and New Moon
Full Moon, New Moon, and the Quarter Moons
Some Wiccans use the word Esbat to describe any Wiccan gathering (especially if ritual or magical work takes place) that doesn't occur on a Sabbat.