Vignette
The edges of a picture darkened toward the corners, drawing the eye to the middle.
See it in FX engine. Under Post-processing, raise Vignette.
In plain words
Old camera lenses let less light reach the corners of the film. The pictures came out darker at the edges. That look is called a vignette. It gently pulls attention to the middle of the frame. Today it is added on purpose, often only a little.