A notch is a small V- or U-shaped cut made into the edge of sheet film. It serves as a tactile guide for photographers, allowing them to identify the orientation of the film in low-light or darkroom conditions without exposing it to light.
In addition to indicating which side of the film is the light-sensitive emulsion side, different notch patterns can also identify the film type or manufacturer. This simple but effective feature is essential for accurate handling and loading of sheet film in large format photography.