Post-crop Vignette
A deliberate darkening or lightening of the frame edges, applied relative to the cropped boundaries rather than the original ones.
Measured in
stops
In depth
Applying it after the crop is what makes it useful — a lens vignette correction is tied to the original frame, but a creative vignette must follow whatever edges the final composition has. Used subtly it holds the eye inside the picture; used heavily it announces itself immediately and dates the image.
Examples in practice
A −0.4 EV post-crop vignette with a wide feather quietly stops the eye drifting out of a portrait's corners.