Often as applied to written work the term "genre" is used pejoratively, suggesting not just similar writings but artificial, derivative,and generally bad writing. Perhaps in connection with this, the term also suggests writing aimed at a particular audience of readers construed as having limited taste. It sometimes connotes a sort of literary "ghetto," to be contrasted with Literature proper.
Only certain sorts of frequently repeated settings and plot devices are labelled "genre fiction," and the selection of the settings so labelled is somewhat arbitrary. Stories about detectives, fantasies about romance, or tales of space aliens are usually considered genre fiction, while tales of Adultery in Academia, My Jewish Childhood, or Beatniks Wandering the Midwest are not considered genre fiction, though in novels they may well be clichés.
Many fiction genres can be traced to a small number of important or extremely popular literary works written before that genre came into existence. "Genre" fiction is portrayed as those works that seek, in some degree, just to emulate these paradigms. Science fiction began with H. G. Wells and Jules Verne. Much, perhaps most fantasy is derivative of--where not plagiarised from--J. R. R. Tolkien's The Lord of the Rings. Horror stories and mystery stories can both be traced in large measure to Poe and a few others.
Many works of undisputed literary merit do in fact bear the characteristic traits of one or another genre. The result is that fans of the genre will tend to treat the work as one of their own and as showing the value of that genre; while those who look down on genre writing will tend to deny that the work in question belongs to that genre at all. Ursula K. Le Guin's The Left Hand of Darkness and Mervyn Peake's Gormenghast are the works of science fiction and fantasy, respectively, most often taken seriously as literature in their own right outside of those genres; correspondingly critics are often hesitant to so classify them. A more extreme example would be Thomas Pynchon's Gravity's Rainbow, widely considered one of the most important novels of the century. It is never called science fiction, despite the fact that a great deal of fictional science is central to its plot.
The word "genre" also applies to film and television, but not to most others arts. On the other hand, popular media that are not generally treated as art are rarely categorized into genres either. This suggests again that "genres" are particularly categories of approaches to arts that are used as a simple tool for producing popular rather than good works.