Mystery fiction is a genre, or category, of fiction that usually involves a murder or crime. Within the category of mysteries are a number of evolving and developing genres bridging true crime, fiction, supernatural, paranormal and others. One of the fun things for a writer is to discover new ways to expand the envelop of a genre, although this may not be so comfortable to the reader.
One of the most popular genres in mystery fiction is what are known as cozy mysteries, or cozies. I have to admit, this is one of my favorite genres.