Contrast ratio is a technical specification which indicates the theoretical contrast you can get with your display, or projector in this story. It’s the difference between light and dark, defined as the ratio between the brightest light to that of the darkest solid black pixel your system can produce. Thus, how much brighter is the light of an all-white image compared to a solid black image? It means that a projector with a 2000:1 contrast ratio will produce its white image 2000 times brighter than the black image.
That’s on paper. But what does it mean if you look at the projected image? Well with higher contrast ratios, the projector reproduces the content with deeper black levels and shadow details. Whereas, with low contrast, blacks or dark areas appear more like grey. The higher the contrast ratio, the sharper the details and the more subtle shades you’ll be able to see. It really boasts the depth of an image and makes it easier to see/recognize objects in darker scenes. All this is especially important when working with high-resolution images and video content.