Fiction in which the
story is guided by the commission and, usually, the
investigation of a
crime. The crime is usually
murder.
Crimefic has many sub-genres: hard-boiled, police procedural, thriller, psychological thriller. Hard-boiled is basically an American thing: when British writers try and do it, they end up looking stupid.
It's widely said that the whole genre was started by Wilkie Collins' The Moonstone in the 1940s, but the first person (that I know of) who was famous as a crime writer was Agatha Christie, from the 1920s onwards. The fact that I hate a lot of her stuff just proves that I'm right to claim that crime fiction is a brilliant representation of the time it was written in.
Being an avid reader of crime fiction is odd. What are you supposed to think of yourself if you get enjoyment from reading about torture, death and dismemberment? You can argue that you read it because it's a genre in which you often get the chance to follow characters over a series of books and see them develop. You can argue that you like the chance to examine moral questions through the medium of the fictional crime. You can argue that crime fiction isn't about real crime, it uses crime as a metaphor for life. You can argue that some of the best writing there is exists in crime fiction. You'd be right on all counts. But that's never going to be the whole story. There's always a sense in which you enjoy seeing people suffer, as long as you're safe, and after all, it's only pretend.