Response time is the amount of time a pixel in an LCD monitor takes to go from black to white and back to black again. It is measured in milliseconds (ms). Lower numbers mean faster transitions and therefore fewer visible image artifacts.
LCD screens with a high response time value are often unsuitable to play fast paced computer games. A response time of <16ms is sufficient for video-gaming[5], and the difference between response times once they're below 10ms begin becoming imperceptible due to limitations of the human eye

The contrast ratio is a measure of a display system, defined as the ratio of the luminance of the brightest color (white) to that of the darkest color (black) that the system is capable of producing. A high contrast ratio is a desired aspect of any display, but with the various methods of measurement for a system or its part, remarkably different measured values can sometimes produce similar results.