The Shankbone or Zeroa in Hebrew, is considered the Passover offering. The Pashcal lamb was sacrificed as the Passover offering.
The sacrifice was done the night the Jewish people were fleeing Egypt from Pharaoh.
The shankbone can be bought at a Kosher butcher and roasted at home over an open flame. All sides should be roasted and any meat should be removed from the bone.
The symbol of the Zeroa is not eaten but refrigerated after the meal to use on the second night of Passover for the second Seder.