A CRT television drew its picture as stacked horizontal lines, an electron beam sweeping left to right, and interlaced broadcasts alternated odd and even lines every field. Up close the image was stripes with dark gaps, softened by phosphor glow. Flat panels erased all of it, and almost immediately graphics began faking it back.
The modern scanline or CRT filter is a post-processing pass: darken alternating rows, add a little horizontal bleed, curve the frame’s corners, maybe a rolling bright bar for the off-sync handheld-camera look, and optionally the RGB phosphor triads that pixel-peeping makes visible. Retro game communities take it further with shader stacks that emulate specific tube models, because pixel art was authored for that glow and looks wrong without it.
As vocabulary the effect says “signal”: surveillance, broadcast, memory, machine vision. It layers naturally with film grain, chromatic aberration, and glitch into the general analog-decay palette. Two cautions carry from craft experience: scanlines against a screen’s real pixel grid invite moiré, so the line spacing needs care, and like every nostalgia effect it works best modulated, surfacing when the music turns cold or mechanical rather than sitting on the whole set.