Cranberry juice is the juice of the cranberry plant, Vaccinum sp. However, due to its incredible tartness, cranberry juice is never sold pure at grocery stores. Instead, it is mixed in with grape, apple or raspberry juices to make it more palatable. Even when strongly diluted, however, cranberry has a distinctive taste that stands out above other juices.
Commercial cranberry cultivation is limited to certain areas of the North America- swampy areas in Oregon, Wisconsin, New England and Quebec, and a small amount of farms in Chile. However, despite the limited growing area, cranberry juice (in its diluted form) costs about as much as apple or grape juice. It is also available for purchase in areas outside of North America.
Cranberry juice has a reputation for having various medicinal properties, most famous of which is its ability to fight bladder infections. The cranberry institute (http://www.cranberryinstitute.org/) lists all sorts of possible medical benefits of cranberry juice, but since they are an organization sponsored by Cranberry growers, they are somehwat biased, but I do suspect that cranberry juice has more than a few hidden beneficient properties.
Cranberry juice, which already comes mixed, is good for mixing further with other beverages, such as ginger ale, 7-Up, other fruit juices, or (for those who drink) whiskey or vodka. I love mixing wine and cranberry juice, although this taste is not exactly widespread.
Impartial says that in Australia, they sell pure cranberry juice in supermarkets.