"Esbat" and "Sabbat" are two terms you come across a lot in witchcraft and paganism, although Esbat tends to be used more in Wiccan circles it is now used across many Pagan paths.
Where as a Sabbat is a celebration of one of the seasonal festivals, an Esbat is a gathering of magical practitioners purely for magical work, often falling on the full moon or new moon.
An Esbat can be used for healing work, initiation rites, or purely to bring together a coven or group of magical practitioners for a social gathering.
The word Esbat is thought to come from the French ébat meaning simply "frolic". This indicates a greater enphasis on socialising and fun than is experienced at Sabbats.