Definition of Yom Kippur
Day of Atonement; is the most sacred and solemn holiday in the Jewish calendar, a day on which Jews throughout the world, after a period of fasting, congregate together at their respective synagogues to worship and pray and ask divine forgiveness for sins committed during the year. Hoffman v. Graber, Mo.App., 153 S.W.2d 817, 818.
That's the definition of Yom Kippur in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.