The Sabbats of Wicca are it's holy days, likened to Christmas and Yom Kippur. There are eight Sabbats that reflect the agricultural cycle of the year. Four of them are refered to as major sabbats and the rest are refered to as minor sabbats. The minor sabbats deal with the Earth's solar orbit, when daylight is longest (Summer Solstice), when the daylight is shortest (Winter Solstice) and when daylight and night are equal (the Equinoxes). The major sabbats are spaced betwen the minor sabbats.
Many Wiccans are gathering together at Sabbats to celebrate together. So there are more and more larger public rituals going on. Some have learned from their mistakes on how to put on rituals that deal with a larger participating body then the traditional coven number of 13. For their advice, please visit the following page: Public Rituals.
If you plan on going to a public event, there are a few things you might wish to learn, such as common ritual etiquitte. For more information on that subject, please visit the following page: Etiquitte.