User blog comment:TheToughGuy/New Projects From TheToughGuy/@comment-4675595-20130814050342/@comment-72.201.2.75-20130814205341

"a la" just means "like."

"AU" is a fanfiction term that means "Alternate Universe" - when you write a fanfiction with a different setting and/or genre than the original work. So "HorrorAU" is just and alternate universe where the story is told in the horror genre.