Chromatic aberration
A post-process effect that offsets the colour channels slightly to mimic the fringing real lenses show toward their edges.
Real lenses bend red, green and blue light by different amounts, so sharp edges pick up a thin colour fringe toward the frame's corners. The effect is faked by sampling the red, green and blue channels with slightly different offsets in a full-screen pass, strongest at the edges. The intent is a cinematic, analogue feel.
Through the 2010s it was applied so liberally it became a running joke — and often the first thing players switch off. Like most depth-of-field and motion-blur effects, it's pure seasoning, not simulation: it adds nothing to the image's information content.