Date arithmetic is simpler to perform in the so-called Julian date format.
This is not a date in the Julian calendar; rather it's a date expressed as a year followed by a 3-digit number representative of the ordinal number of the day in the year.
Conversely, a date containing a year, a 2-digit month and a 2-digit year is sometimes called Gregorian, even though both dates are in the Gregorian calendar.
The fruit of the Date Palm, or the Chinese Date which is a Jujube.
Dating can refer to the determination of the approximate period of origin of an object, particularly in the case of historical or archeological finds such as antiques or fossils.
Dated, as an adjective, refers to something that is, or appears to be, old or otherwise out of style.