Overexposed image areas with zero detail — highlights blown to pure white. Either mistake or intentional choice for graphic contrast.
When the highlights completely lose detail, it's called being blown out. The light has overloaded the sensor sensitivity or film emulsion to such an extent that there is no longer any tonal gradation in the bright areas – only pure white. On the monitor, this appears as a flat, featureless area; in the histogram, the curve climbs to the right edge and disappears there.
In practical work on set, this is usually a problem. You light a scene, the actors are standing in front of a bright window, and suddenly the faces are correctly exposed, but the sky outside is completely empty – white, without any gradation. This cannot be salvaged in the edit. Therefore, you constantly monitor the histogram and the highlights on the monitor. For critical shots – such as portraits with backlight or interiors with sunny exterior light – you must either lower the exposure (aperture, ND filter, ISO), modify the light, or work with Exposure Bracketing to blend later.
However, being blown out isn't always a mistake. Some cinematographers and directors consciously use it as a stylistic device – extreme high-key scenes, flashbacks in blindingly white rooms, or to achieve an almost documentary contrast. Austrian cinematographer Hoyte van Hoytema deliberately provoked this in some sequences of *Dunkirk* to convey disorientation under fire. This is then not a mistake, but conscious design.
Modern digital technology makes it easier to play with clipping: RAW footage often still offers reserves in the highlights that the codec initially hid. But lost is lost – as soon as the pixel is completely saturated, even the best colorist can't help. Hence the old rule of thumb: "Expose for the shadows, grade the highlights." You expose for the dark areas, but aggressively monitor that the highlights still retain detail. The margin is narrow, and every decision on set counts.