Yom Kippur, or The Day of Atonement, is the Jewish holiday when, following Rosh Hashanah, the new year in the Jewish calendar, a ten-day period of self-evaluation and repentance culminates in a public recitation of sins. If successful, the Jew is "inscribed" in the book of life for another year of life. The ten-day period is call the Ten Days of Repentance.
Yom Kippur, besides the Sabbath, is the holiest day in the Jewish calendar. It is marked by fasting and, for Orthodox Jews, day-long attendance in the synagogue. The holiday begins with the Kol Nidre service on the previous day at sundown, the eve of Yom Kippur.