What is a date?
A (calender) date does reference to a particular date back or forth in time. The date is always just valid for the corresponding calender system. Dates can be converted from one calender system to another. The exact date of an event is furthermore dependent on the different time zones. The date of the Pearl Harbor attack for example took place on the 7th December 1941 Hawaian time, in Japan time was alredy the 8th December. In many calender systems the date has the following parts: day (of month), month and the year. Additonally there also can be the day of the week.