It is called Photosensitive film or  Photographic film or PCB mask also known as dry film. This sheet is used to produce high quality PCB tracks in a simple and clean way. Just stick it on top of the PCB, it will become a sensitive circuit board. Next, expose the pcb with the film to UV light source (the sunlight for example) and you will have the required tracks impressed on the pcb.

Watch the youtube video below for clear and detailed procedures for manufacturing PCB at home using photosensitive film.