Yom Kippur (Day of Atonement) is the holiest day in Judaism, observed on the 10th day of Tishrei. It concludes the Ten Days of Repentance that begin with Rosh Hashanah.
Established in the Torah (Leviticus 23:26-32). Yom Kippur was the only day the High Priest entered the Holy of Holies in the Jerusalem Temple. After the Temple's destruction, prayer and personal repentance replaced the Temple service.
25-hour fast (no food, water, leather shoes, bathing, or sexual relations) for adults. All-day synagogue services include Kol Nidre (evening), Yizkor (memorial), and Neilah (closing). White clothing worn to symbolize purity.
Pre-fast meal ("seudah hamafseket") is typically simple and bland (to ease the fast). Break-fast after sundown often features bagels, lox, kugel, and dairy dishes.
"Yom Tov" · "Gmar Hatima Tova" (May you be sealed for good)
In Israel, Yom Kippur is the strictest holiday. The entire country shuts down — no traffic on highways (a remarkable annual sight), airport closes, broadcasting silent, no commerce. Children bicycle freely on empty streets in many cities.