The novel is an extended work of prose fiction. It derives from the Italian novella (“little new thing”), which was a short piece of prose. The novel has become a popular form of fiction since the early 18th century, even if prose narratives were written long before then. The term refers to a prose narrative about characters and their actions in what is recognisably everyday life. This differentiates it from its immediate predecessor, the romance, which describes unrealistic adventures of supernatural heroes. The novel has developed various sub-genres. Read here and here.
You can also read this post about the various genres of fiction.