Yom Kippur is a Jewish festival. It is also known as the "Day of Atonement". It lasts 25 hours. During this period, Jews ask God to forgive them for all their sins. People fast on this day, and they go to synagogue. Other things people are not allowed to do during Yom Kippur include washing, using perfumes and lotions. Many wear white as a symbol of purity. Even though people fast, Yom Kippur is considered a happy holiday. This is because Jews are sure that God will forgive them on this day.