(history) A year in the old Julian calendar (which started on different dates).
(astronomy) An "average year" of 365 days and six hours, used for convenience of quick calculations, as opposed to a calendar year of either 365 or 366 days, and a mean tropical year of 365 days, 5 hours, 48 minutes and 45 seconds.
Through a like want of attention, many writers also, particularly among the moderns, have confounded the Julian and Olympic years, by making an entire Julian year correspond to an entire Olympic year, as if both had commenced at the same epoch.
The adoption of the Julian year must therefore have taken place about 160 years before the year 136 of our era (the difference between the Egyptian and Julian years being one day in four years), that is to say, about the year 25 B.C. In fact, the first of Thoth corresponded with the 29th of August in the Julian calendar, in the years 25, 24, 23 and 22 B.C.
Some authors who follow the Macedonian era, use the Egyptian or vague year of 365 days; Albategni adopts the Julian year of 3654 days.
According to the computation most generally followed, the year 312 of the era of the Seleucidae began on the ist of September in the Julian year preceding the first of our era.
The year thus became exactly similar to the Julian year.