Yom Kippur

Yom Kippur, also known as the Day of Atonement, is perhaps the most important holiday of Judaism. During Yom Kippur you are to abstain from eating, drinking, wearing leather shoes, bathing or washing, putting on perfumes or lotion, and marital relations--better known as sex. Of course, these restrictions may be levied if they inflict upon ones life or health. For example, young children (under the age of 9) and pregnant women may not fast, even if they wish to do so. On this day, as the name would suggest, those who practice Judaism atone for their sins over the past year. Most of the holiday is spent in the synagogue, praying. It is also customary to wear white on this holiday.

http://www.jewishvirtuallibrary.org/jsource/Judaism/holiday4.html