Day of Atonement

Yom Kippur
Jews Praying in the Synagogue on Yom Kippur, by Maurycy Gottlieb (1878) Hebrew: יוֹם כִּיפּוּר‎‎ or יום הכיפורים
Observed by	Jews, Samaritans, some Christian groups
Type	Jewish
Significance	Atonement for personal and national sins, fate of each person is sealed for the upcoming year
Observances	Fasting, prayer, abstaining from physical pleasures, refraining from work
Date	10th day of Tishrei
2016 date	sunset, October 11 – nightfall, October 12. Karaite: same
2017 date	sunset, September 29 – nightfall, September 30.
Related to	Rosh Hashanah, which precedes Yom Kippur

Yom Kippur (/jɔːm, joʊm, jɒm ˈkɪpər, kɪˈpʊər/;Hebrew: יוֹם כִּיפּוּר‎, IPA: [ˈjom kiˈpuʁ], or יום הכיפורים‎), also known as the Day of Atonement, is the holiest day of the year in Judaism. 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", which is related to the biblical name of the covering of the Ark (called the kapporet). Yom Kippur is usually expressed in English as "Day of Atonement".