What is "nychthemeron"

n. A period of one day and one night, a date: in the West, this is a period of 24 consecutive hours.

Nychthemeron , occasionally nycthemeron or nuchthemeron (Greek νυχθήμερον from the words nykt- "night", and hemera "day, daytime"), is a period of 24 consecutive hours. It is sometimes used, especially in technical literature, to avoid the ambiguity inherent in the term day.

It is the period of time that a calendar normally labels with a date, although a nychthemeron simply designates a time-span that can start at any time, not just midnight.