Derived from Latin annus are a number of English words, such as annual, annuity, anniversary, etc.; per annum means "each year", anno Domini means "in the year of the Lord".
The Greek word for "year", , is cognate with Latin vetus "old", from the PIE word *wetos- "year", also preserved in this meaning in Sanskrit vat-sa-ras "year" and vat-sa- "yearling (calf)", the latter also reflected in Latin vitulus "bull calf", English wether "ram" (Old English weðer, Gothic wiþrus "lamb").
In a non-leap year, there are 365 days, in a leap year there are 366 days.
A leap year occurs every fourth year, or leap year, during which a leap day is intercalated into the month of February. The Gregorian calendar attempts to cause the northward equinox to fall on or shortly before March 21 and hence it follows the northward equinox year, or tropical year. It is estimated that by the year 4000 CE, the northward equinox will fall back by one day in the Gregorian calendar, not because of this difference, but due to the slowing of the Earth's rotation and the associated lengthening of the day.
A revised chronology, based on detailed Bayesian modelling, is presented for the Lower Tilemsi region.
Dates in this era are designated Anno Domini (Latin for in the year of the Lord), abbreviated AD, or the secular common era, abbreviated CE.
The word "year" is also used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year, the academic year, etc.
Similarly, "year" can mean the orbital period of any planet: for example, a Martian year or a Venusian year are examples of the time a planet takes to transit one complete orbit.
The Revised Julian calendar, as used in some Eastern Orthodox Churches, currently does a better job than the Gregorian in synchronizing with the mean tropical year.
As 218 out of every 900 years are leap years, the average (mean) length of this Julian year is A calendar era assigns a cardinal number to each sequential year, using a reference point in the past as the beginning of the era.