A more thorough explanation:

NYCHTHEMERON

A nychthemeron is a 24-hour period that includes both day and night.

One example of a nychthemeron is a typical day, from midnight to midnight. Another example is a work shift that starts in the evening and ends the next evening.

These examples illustrate the definition of a nychthemeron because they both encompass a full day and night, totaling 24 hours. The term is often used in scientific or medical contexts to describe the duration of certain processes or cycles.