Yom Kippur (Hebrew: יוֹם כִּפּוּר, IPA: [ˈjom kiˈpuʁ], or יום הכיפורים), also known as Day of Atonement, is the holiest day of the year for the Jewish people. Its central themes are atonement and repentance. Jewish people traditionally observe this holy day with an approximate 25-hour period of fasting and intensive prayer, often spending most of the day in synagogue services.
Yom means "day" in Hebrew and Kippur comes from a root that means "to atone". Thus Yom Kippur has come to mean "day of atonement". Some say there is a link to kapporet, the “mercy seat” or covering of the Ark of the Covenant. Abraham Ibn Ezra states that the word indicates the task and not just the shape of the ark cover; since the blood of the Yom Kippur sacrifice was sprinkled in its direction, it was the symbol of propitiation.
Yom Kippur is "the tenth day of [the] seventh month" (Tishrei) and also regarded as the "Sabbath of Sabbaths". Rosh Hashanah (referred to in the Torah as Yom Teruah) is the first day of that month according to the Hebrew calendar.