What is "eid-e-shuja'"

Eid-e-Shuja', also known as Eid-e-Zahra, is a ritual festival observed by most Twelver Shi‘a Muslims. It marks the end of the two-month mourning period (azadari) after the events of the Karbala massacre, which occurred in 680 AD (61 AH). It is celebrated annually on the ninth day of the month of Rabi' al-Awwal in the Islamic-Hijri calendar.