Film is a means of communication and any means of communication has a language. The language of film communicates in many ways, through costume, casting, dialogue, music, sets, editing, camerawork - a combination of signs specific to the techniques of film making, drawing on our own experiences and knowledge of the world.
Semiotics is the study of signs and their operation in codes. It is applicable to language itself and to any cultural phenomena, from film to fashion. In semiotic terminology, messages and meanings are coded or encoded in cultural products, to be decoded by audiences.
Ideologies are able to operate through discourse. Discourse theory requires us to grasp the fact that we do not merely use language as a neutral medium of exchange in which to conduct or reflect on our social life.
Our social life is the language in which we conduct it. Through discourse, the relations between groups and classes are constantly being re-negotiated.