In programation, the raster is often referred as the act to modify the setting of inks between 2 scanlines, in interrupt mode.
This is a way to display more than the usual [[Video modes]] number of colours.
So It has enough cycles between 2 scanlines to order this.
You can also use Split rasterto raster to "actually" display 2 different screens, sometoimes sometimes with different Video Modes. This also allows a Graphic heavy [[HUD]] with no interference with [[Scrolling]].