Someone that needs to drink blood to survive. Personally I always thought being one has more drawbacks than anything, and their mythos gets more and more convoluted the more time passes by. Basically, feeding on other people makes them stronger and immortal.

[Poor girl is going to have no idea what Luz is talking about. Luz is unfortunately VERY familiar with vampires now, having been bit by one].

Oh, Robyn? No, not at all! So if you bit me, when I sleep I become a wolf, right?