1. the opposition or dissimilarity of things that are compared;
"in contrast to", "by contrast"
2. the act of distinguishing by comparing differences
3. a conceptual separation or demarcation;
"there is a narrow line between sanity and insanity"
4. the perceptual effect of the juxtaposition of very different colors
5. the range of optical density and tone on a photographic negative or print (or the extent to which adjacent areas on a television screen differ in brightness)