The scanline renderer renders the scene as a series of horizontal lines. It is one of the production renderers provided with 3ds Max, as opposed to the interactive renderer used in viewports. Images produced by production renderers display in the rendered frame window, a separate window with its own controls.
The scanline renderer is the original 3ds Max renderer, and it is the default production renderer choice when you first use the Render Setup dialog or from Video Post.
For more general information, see Renderers.