1 Palpatine: There is a great disturbance in the Force.
1 Vader: I have felt it.
2 Palpatine: We have a new enemy. Luke Skywalker.
2 Vader: Yes, my master.
3 Palpatine: He died in the assault on Hoth, but I hear he rose as a vampire.
3 Vader: Yes. We need a cleric.
4 Palpatine: A cleric?
4 Vader: If he could be turned, he would become a powerful ally.

Turning undead is a power available to members of the cleric class in Dungeons & Dragons. The cleric presents a holy symbol forcefully towards undead monsters (such as skeletons, zombies, ghouls, vampires, etc.) and, usually if a dice roll is made successfully, the undead will be forced to flee rather than attack.

Many media have copied the idea from D&D, which itself got the idea from cinematic vampire lore - the image of a person holding a vampire at bay by brandishing a Christian cross at it.