A light novel (Japanese: ライトノベル, Hepburn: raito noberu) is a type of popular literature novel from Japan usually classified as young adult fiction, generally targeting teens to twenties or older. The definition is very vague, and wide-ranging but it generally refers to a story accompanied with manga-style illustrations, often in black and white.

Lots of manga and anime are based on light novels. They often have a lot of volumes. For example, my favorite LN is Ascendance of a Bookworm, whose main story has 33 volumes.