Shabbat - The Sabbath

Jewish law accords the Sabbath the status of a holiday. Jews celebrate a Shabbat, a day of rest, on the seventh day of each week. Jewish law defines a day as ending at nightfall, which is when the next day then begins. Thus, Shabbat begins at sundown Friday night, and ends at nightfall Saturday night.

In many ways halakha (Jewish law) gives Shabbat the status of being the most important holy day in the Jewish calendar.

(Adapted from Wikipedia)