Here is a little introductory statement from Barry Keith Grant concerning genre:
Stated simply, genre movies are those commercial feature films which, through repetition and varitation, tell familiar stories with familiar characters in familiar situations. They also encourage expectations and experiences similar to those of similar films we have already seen. Genre movies have impressed the bulk of film practice, the iceberg of film history beneath the visible tip that in the past has commonly been understood as film art. They have been exceptionally significant as well in esrablisjing the popular sense of cinema as a cultural and economic institutions, particularly in the United States, where Hollywood studios early on adopted an industrial model based on mass production. Traditionally, Hollywood movies have been produced in a profit-motivated studio system which, as the result of sound business practice, had sought to guarantee acceptance at the box office by the exploitation and variation of commercially successful formulas. In this system, praised for the “genius” of its efficiency by Andre Bazin, genre movies are the Model T’s or the Colt revolvers with interchangeable parts.1
1. Barry Keith Grant (ed), Film Genre Reader II, Austin: University of Texas Press (1999), p. XV.