Brandiwyn🎶 may have a different idea, so she should also answer.

But an anti-hero is when the book is centered around a character that is NOT the hero of the story. I looked up the definition, and I'm not pleased when it simply talks about someone who lacks the hero qualities. Ugh.

So... a couple examples
Gone Girl - Nick and Amy are the main characters. No heroes here, just twisted dark characters trying to get to their own ideals.
My friend Shannon Ryan writes great anti-heroes. They're all slackers who don't want to get pulled into the action and only go along with it because there's really no other choice. Most of the time they're only successful because of an accident. (I think of you, Waltz Invictus , sometimes when I read them. I mean, a Satanic cult who fronts a call center? Brilliant.)
Lolita is a famous example of an extremely unlikable main character.

We're much more familiar with heroes: Harry Potter has Harry Potter- he's brave and he pulls out random spells and he and his team manage to vanquish the evil guy. Many fantasy stories have that hero, the underdog who is going to right the big evil in the world an goes on a quest to do this. So we're looking for stories where the protagonist is unlikeable, where the protagonist might be a bad person, where they lack qualities that lead them to be great main characters.