The contrast ratio is defined as the ratio of the luminance of the brightest colour (white) to that of the darkest colour (black) that the system is capable of recording. A high contrast ratio is a desired aspect of any camera system.
Static contrast ratio is the luminosity ratio comparing the brightest and darkest colour the system is capable of recording simultaneously at any instant of time, while dynamic contrast ratio is the luminosity ratio comparing the brightest and darkest colour the system is capable of recording over time (while the picture is moving). Moving from a system that records a static motionless image to a system that records a dynamic, changing picture slightly complicates the definition of the contrast ratio, due to the need to take into account the extra temporal dimension to the measuring process.
There is no official, standardised way to measure contrast ratio for a system or its parts, nor is there a standard for defining "Contrast Ratio" that is accepted by any standards organisation so ratings provided by different manufacturers of display devices are not necessarily comparable to each other due to differences in method of measurement, operation, and unstated variables.
Also see dynamic range.