Yom Kippur, the Day of Atonement, falls ten days after Rosh Hashanah. When the Temple stood in Jerusalem, the High Priest effected atonement for the entire people through an elaborate ritual. Today, in the absence of the Temple, each of us stands, alone, together, naked as it were, before God.
Yom Kippur is the dramatic culmination of the entire season of teshuvah, repentance. On Yom Kippur, Jews abstain from eating, drinking, bathing, sexual relations, and the wearing of leather (a sign of luxury) for 25 hours. Jews dress in white and traditionally spend most of the day in synagogue.