Yom Kippur, also known in English as the Day of Atonement, is the most solemn and important of the Jewish holidays. Its central themes are atonement and repentance. Jews have traditionally observed this holiday with a 24-hour period of fasting and intensive prayer. Total abstention from food and drink usually begins 30 minutes before sundown , and ends after nightfall the following day. Although the fast is required of all healthy adults, it is waived in the case of certain medical conditions. Virtually all Jewish holidays involve a ritual feast, but since Yom Kippur involves fasting, Jewish law requires one to eat a large and festive meal on the afternoon before Yom Kippur.