is the name for the first day of every month in the Hebrew calendar, marked by the appearance of the New Moon. It is considered a minor holiday, akin to the intermediate days of Passover and Sukkot.

Tisha B'Av, the Fast of the Ninth of Av, is a day of mourning to commemorate the many tragedies that have befallen the Jewish people, many of which coincidentally have occurred on the ninth of Av. Tisha B'Av primarily commemorates the destruction of the first and second Temples, both of which were destroyed on the ninth of Av (the first by the Babylonians in 586 B.C.E.; the second by the Romans in 70 C.E.).