Contrast ratio refers to the difference between the minimum brightness and maximum brightness of a monitor. For example, looking at a monitor with a 1,000:1 contrast ratio, a white image would appear 1,000 times brighter than a black image on a particular monitor. A higher contrast ratio, in theory, should produce deeper blacks with increased grayscale detail. In addition, a higher contrast ratio means that scenes that are supposed to be black or dark are more lifelike and don't appear washed out (i.e., shadows look more gray than black).
OLED (organic light-emitting diode) displays are promoted as having an infinite contrast ratio because the self-lit pixels can turn completely off to present a perfect black. IPS (in-plane switch) displays usually hover around the 1,000:1 mark or slightly higher, while VA (vertical alignment) displays can range from 3,000:1 to 4,000:1 at the high-end.
This article is part of the Tom's Hardware Glossary.
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