In packaging and bag terminology, film means a thin, flexible plastic sheet. Both the bag itself and the surface that is printed on are film. Polyethylene film is usually produced by the blown method: the melt leaves an annular die as a tube, is inflated, cooled and flattened.
The flattened bubble can be wound as a two-layer tubular film, or slit along its edges to become single-layer film. Film can be single-layer or made of several layers by co-extrusion. Its thickness is expressed in microns. Which bag a film becomes is determined by its raw material, its thickness and the printing and cutting steps that follow.