The Holy medallion of Karra are medallions given to those who are chosen as Honored Ones to fulfill the Wraithfall ceremony. Five Karrans are chosen ever three months. After the Honored Ones get their medallion, they are then culled into a Wraith Dart. (SGA: "Wraithfall 1")
Those with the medallion are then taken to an Experimental laboratory on Vohl to undergo experiments that enhances the Wraith feeding process.
Getting the medallion of Karra is seen as the highest honor among the Karrans. (SGA: "Wraithfall 2")