A date in a calendar is a reference to a particular day by means of a calendar system. The calendar date allows the particular day to be identified. One can often determine how many days one date comes after another date. For example February 17, 2003, is ten days after February 7, 2003, in the Gregorian calendar.
In most calendar systems the date consists of three parts: the year, the month and the day of month. There may also be additional parts, such as the day of week. Years are usually counted from a particular starting point, usually called an era, but sometimes an epoch.
A date with the year part removed may also be referred to as a date or calendar date (e.g. February 7 rather than February 7, 2003). As such it defines the days of an annual festival such as a Birthday or Christmas on December 25th.
Related to the classification of a day as a specific calendar date, is the format used to express that date.
Even for one calendar system, different formats are used. For example, the following formats all express the same date in the Gregorian calendar:
These are further complicated by the common practice of abbreviating the year to its final two digits, and/or abbreviating the full name of the month to its initial three letters.
A significant amount of confusion arises from the ambiguity of a date order; especially with low day, month and/or year numbers, it is impossible to tell which order is being used. Various schemes are used to correct these ambiguities; common schemes include spelling out the month name (or its abbreviation) and using four-digit years. The ISO 8601 date order, with four digit years, is specifically chosen to be unambiguous.
Some argue that the m/d/y order is illogical, as it does not give the units in order of size, either increasing (d/m/y) or decreasing (y/m/d).
d/m/y (day, month, year) is used by:
m/d/y (month, day, year) is used by:
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