Cut executed as focus pulls past sharp area — lens drifts microns out, creating imperceptible glitch or visual jolt. Usually accident, sometimes intentional.
You notice it immediately when it happens: the focus drifts by a hair's breadth past the plane of focus, and for a quarter of a second — sometimes just two frames — you lose control of the image. That's grazing. Not completely out of focus, not dramatic — just that imperceptible unease that the viewer can't name but feels. On set, we call it the moment the focus puller blinks.
In practice, grazing usually happens unintentionally. A camera movement that was miscalculated by a minimal amount. An actor who positions themselves a centimeter closer than agreed upon. Or simply: the depth of field is so shallow — for example, at 24mm, aperture 1.4, on full frame — that any minimal tracking error by the focus puller creates this irritation. It becomes particularly treacherous with fast zoom lenses or long focal lengths: there, even millimeter errors add up to visible disturbances. You often only see it in playback after the take is over.
Sometimes grazing is used intentionally. Some DoPs use it deliberately — for example, to create psychological tension when a character is just slipping out of focus, or to evoke unease without it appearing like a deliberate focus error. However, this requires discipline and timing. In the edit, grazing can hardly be salvaged afterward: you can stabilize it, but not correct it. That's why it's a nightmare on set — too small to simply reshoot, too distracting to ignore.
The best defense: factor in sufficient depth of field in the shooting plan, check with the focus puller early on for critical movements, and exercise extra care with markings at shallow apertures. Some teams also use wireless follow-focus systems for particularly tricky takes — this reduces human error rates but never completely eliminates grazing. It remains one of the subtler pitfalls between technique and creation.