The Ninth of Av is a day of mourning in the Jewish calendar. It commemorates the destruction of the First and Second Temples in Jerusalem and other tragedies that have befallen the Jewish people throughout history. This day is also known as Tisha B'Av. The word "Tisha" in Hebrew means "nine", referring to the ninth day of the month of Av. Some synonyms for Ninth of Av are Day of Mourning, Day of Atonement, and Fast Day. It is customary for Jews to fast and refrain from other activities on this day to show their respect for the tragedies that have occurred in Jewish history.