The tag YA is very popular among bloggers who review books for young adults and by people discussing young adult literature, such as parents, teachers, librarians, book award committees, and booksellers. The tag is also often used by the YA authors, illustrators, editors and publishers who create literature for young adults. There are many web sites, professional organizations, and courses dedicated to young adult literature.
It is generally thought that books referred to as YA are for young readers age thirteen and above. Books for readers under thirteen are referred to as children's books. YA literature is most often categorized by genre, such as biography, fantasy & science fiction, non-fiction, and poetry.
Regardless of how they are categorized, many books termed YA literature are read and enjoyed by adults, such as the Twilight series by Stephenie Meyer.