Mystery fiction is a loosely-defined term.

1.It is often used as a synonym for detective fiction

Detective fiction

Detective fiction is a sub-genre of crime fiction and mystery fiction in which an investigator , either professional or amateur, investigates a crime, often murder.-In ancient literature:...

 or crime fiction

Crime fiction

Crime fiction is the literary genre that fictionalizes crimes, their detection, criminals and their motives. It is usually distinguished from mainstream fiction and other genres such as science fiction or historical fiction, but boundaries can be, and indeed are, blurred...

— in other words a novel or short story in which a detective (either professional or amateur) investigates and solves a crime mystery. Sometimes mystery books are nonfiction. The term "mystery fiction" may sometimes be limited to the subset of detective stories in which the emphasis is on the puzzle/suspense element and its logical solution (cf.