In the Eastern Orthodox faith, days that commemorate a particular saint, holy event, or the angels are called feast days. Is it called a feast day because there is a feast? No. Can food be part of the equation? Yes.
September 8th is the feast day of the Nativity (birth) of the Virgin Mary. In Greek Orthodox tradition, feast days are holy days that commemorate significant events related to the church. They may mark the births and/or deaths of saints, or other momentous occasions. This particular feast day marks the day that Orthodox Christians commemorate the birth of the Virgin Mary. In Greek she is called the Theotokos, or Mother of God.