Yom Kippur is the Day of Atonement and considered one of the two holiest days in the Jewish calendar, along with Rosh Hashanah. Jewish families may observe Yom Kippur by fasting for a full day from sundown to sundown, refraining from work, and attending synagogue services. Source: Blakemore, E. (2021, September 14). Why Yom Kippur is the holiest day of the Jewish year. History. https://www.nationalgeographic.com/history/article/yom-kippur-history-traditions