The proper term for this effect is "raster bars", from how you traditionally did the effect by waiting for the raster line register to hit a certain vertical position on the screen, and then changing f.e. the background color of that scanline, then wait for the next line, change the color again etc. The name "copper bars" came out of the Amiga scene from how you could easily and without involving the CPU do this effect (and much more) on the Amiga using one of its co-processors, nicknamed the "Copper".