Tisha B’Av is a solemn Jewish fast day that commemorates the destruction of the First and Second Temples in Jerusalem, along with other tragedies in Jewish history. It is observed with a 25-hour fast, mourning rituals, the reading of the Book of Lamentations, and sitting on the floor or low stools in grief. The day reflects themes of loss, exile, and the hope for future redemption and rebuilding.