A group of ships in the Avatar: The Last Airbender universe which can mean any combination of ships between Zuko or Azula with any of their family members, such as Ozai, Ursa, Iroh, eachother, etc. Regardless, its an incest ship involving two members of the Fire Nation royal family.
The most commonly referenced ship in this group is Zuko/Azula, based on perceived sexual tension between Zuko and Azula in certain scenes in the series, and based on minority fan speculation that Azula's desire for dominance and manipulation over Zuko is sexual as well as severe sibling rivalry (based on stretched but still viable examples, such as Azula's focus on Zuko, her consistent use of the nickname "Zuzu" throughout the series, as well as the bedroom dialogue scene in Book 3 episode 1 "Awakening")
1. "Dude, why is Azula always talking about facing Zuko and not Iroh in Book 2? That kind of obsession is a good argument for Zucest!"
2. "Azula has some strong fixation on pleasing her dad. You think there's zucest going on there?"
3. "Iroh's and Zuko's closeness SO borderlines on Zucest!"