Final answer:
The ratio between the vertical resolution and the number of horizontal scan lines in a television system is called the Kell factor, which relates to the perceived image quality on the screen.
Step-by-step explanation:
The ratio between the vertical resolution and the number of horizontal scan lines in a television system is known not as a conversion factor, but as the Kell factor. The Kell factor takes into account the detail that can be perceived in the vertical dimension relative to the fixed number of horizontal lines. This concept differs from a magnification or a resolution factor, which both refer to the clarity or the size of an image compared to the original. In television systems, the Kell factor affects the overall visual resolution that the viewer perceives on the screen, thus impacting the quality of the image display.