The day of atonement. This is the day where our decree for the future of that year is sealed. This day has a violation of Karet if violated in any way, shape, or form. The same Halachot as Shabbat, but you cannot eat unless it is life, or death, or a highly severe sickness. Women are also obligated to fast on this day. Children under the age of 13 don't have to, but it is recommended for them to. We pray, and cry most of this day to get a good decree in Shamayim!