Standard 35 mm film has individual frames with the size 36 mm by 24 mm. It is by far the most common film format for amateur photography, though digital cameras are improving in quality and becoming much more common. Edison's Kinetoscope, invented in 1889, set 35 mm as the standard. Legend has it that when Edison was asked by his workers how wide to cut the film (which was manufactured by the Eastman company), he held up his thumb and forefinger and said "About this wide."
More probable, however, is that the 35 mm width was derived by just slitting in half the readily available 70 mm wide Eastman roll film (unperforated, used for still-pictures). Supposedly 35 mm film was once even called Edison size.