Adult fiction is a category or genre of books used to describe fictional writings that are designed for adult readers. Many authors write books for specific age groups and even demographics -- young children, kids, tweens, teenagers, young adults, and adults; as well as working-class citizens, high-class citizens, low-class citizens, etc. The writing style and plot of a story will definitely help define the audience it should be read by. Adult fiction is arguably one of the most popular genres of books out there. Most adults admit to enjoying fictional books and narratives when they're not working; these types of books are easier to start and stop and put down at a moment's notice; also, the flow of writing is easier to pick up again if you find yourself dealing with a lot of distractions.
Adult fiction is one genre of book that you will have no trouble finding. All bookstores will have a very large selection of adult fiction that may be further broken down by genre (romance, mystery, horror, science fiction, etc.). Dollar stores, grocery stores and retail stores also often carry some books for their customers to purchase, and you may very well be able to find some adult fiction selections mixed in.
Fiction Online