It is one of the worlds involved in the Twine Wars.
Shade is a nickname short for a phrase beginning Shade of a grove of trees, used by demonic visitors to refer to the world (which they, for various reasons, consider a pleasant shelter). The name Shade may not catch on universally among inhabitants but will end up as the default name for the world among other Twine Wars worlds. Most of the time Shade's residents call it simply 'the world', unless they're distinguishing it from others.
Historical note: Traditionally, the two powers of the northern hemisphere (which became Soprone and the Pais Meizurs) considered a day to last betwen sunrise and sunset. The period of darkness was considered 'in between' one day and the next; it was not considered a day in itself. The 18-hour subdivision and sunrise-to-sunrise convention spread from Induba.
See also: