[Brightcolours]

Lets describe contrast as a difference between pixel values (black white, red green, blue yellow) and dynamic range as the possible maximum and minimum color value at the same time. So it is described as difference too. But if people speak about contast they are describing mostly the local contrast. Local contrast could be described a very low frequency like sharpness is a high frequency. So global contrast is dynamic range local contrast is something different and depend of high dynamic range values and resolution so you can increase the contrast of clouds for example. But we are now really of topic.

High DR means that the white point and the black point lay as far from eachother as possible. With high contrast they lay very close to eachother. 

High DR = low contrast

Low DR = high contrast.