Djent is basically a style of music where the guitars are tuned to like h flat and you only need one string and 3 frets, also you need like 7 noise gates, an 8 string guitar (cause 7 is for pussies), axe effects, and atmospheric sections.
The genre of Pig Heart Boy is 'Children's'. You may think that 'Children's' is not really a genre but its also a genre ifthe book is turned into a series or a film then the genre will be different to a normail genre of a book.
The prefix sub- means "under," or "lesser." A sub-genre is a genre within a genre, that is a specific category within a more general one. For example, within the genre of Juvenalia, or "children's literature," a sub-genre might be books specifically intended for pre-teen boys.
The word "genre" is basically synonymous with "catagory" -- e.g., That painter works in the genre of seascapes. His sister works in the still life genre. Even more familiar would be with reference to movies -- the horror genre, the sci-fi genre, etc.