As Runed Halo enters the battlefield, choose a card name.
You have protection from the chosen card name. (You can't be targeted, dealt damage, or enchanted by anything with that name.)
Runed Halo can't protect you from tokens unless those tokens have the same name as the card name you choose.
Some cards can have alternative names, such as split cards, adventurer cards, double-faced cards, and so on. You may choose one of the two names the card can have; Runed Halo won't protect you from the other name.