In general terms, the measure of the light-gathering power of silver or dye deposits in film. Also, the buildup of silver that creates the image in film and paper. A dense negative or slide is more opaque than a thin one. There is an ideal density for film, one that yields good prints or slides too little density usually means that the film was underexposed (or underdeveloped), too much means its been overexposed (or overdeveloped).