Ashura (Arabic: عاشوراء) falls on the 10th day of Muharram, the first month of the Islamic calendar. For Shia Muslims, it commemorates the martyrdom of Imam Hussein at the Battle of Karbala in 680 CE. For Sunni Muslims, it commemorates the day Moses and the Israelites were saved from Pharaoh.
The Sunni significance traces to Prophet Muhammad, who reportedly observed the day after seeing Jews of Medina fasting in commemoration of Moses. The Shia significance was profoundly shaped by the killing of Hussein, grandson of the Prophet, at Karbala — a foundational moment in Shia identity.
Sunni Muslims observe a recommended (but not mandatory) fast. Shia Muslims hold solemn processions of mourning (matam), reenact the Karbala story (Ta'zieh), and visit Hussein's shrine in Karbala (the world's largest annual pilgrimage by foot, surpassing Hajj in attendance). Some Shia traditions include self-flagellation, though many religious leaders discourage it.
Shia communities serve traditional foods to mourners — ash-e-soltani (Iranian soup), various stews. Sunni traditions vary.
Public holiday in many Muslim-majority countries. Karbala in Iraq sees over 20 million pilgrims for Arba'in (40 days after Ashura).
Future dates for moving holidays (Easter, Eid, Lunar New Year, Diwali, etc.) are computed and approximate; the actual public-holiday date in some countries is fixed by official decree closer to the date.