From Shuushuu

Light novels are small, Japanese books. They often include some illustrations interspersed between chapters, though they do not have to. These books are generally intended for young adult readers more than adult, and are very popular in Japan. Unfortunately, while some of these novels are translated and sent overseas, not as many are as manga.

Light novels have a very "light", easy to read writing style and are intended for entertainment purposes. Paragraphs are short and dialogue abounds in these books, and the pacing tends to be slow.