What is a date?
A (calender) date refers to a particular date back or forth in time. It is valid only for the corresponding calender system. Dates can be converted from one system to another. Furthermore, the dates of events may vary depending on different time zones. The Pearl Harbor attack, for instance, took place on the 7th December 1941 Hawaiin time, but in Japan, it was already the 8th December. In many calendar systems, the date consists of the day (of the month), the month, and the year. In addition, the weekday is often included as well.