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 the Julian calendar, the average (mean) length of a year is 365.25 days.
In a non-leap year, there are 365 days, in a leap year there are 366 days.
The term can also be used in reference to any long period or cycle, such as the Great Year.
(hṓra) "year, season, period of time" (whence "hour"), Old Church Slavonic jarŭ, and Latin hornus "of this year".
For the Gregorian calendar the average length of the calendar year (the mean year) across the complete leap cycle of 400 years is 365.2425 days.
The ISO standard ISO 80000-3, Annex C, supports the symbol "a" (for Latin annus) to represent a year of either 365 or 366 days.
Financial and scientific calculations often use a 365-day calendar to simplify daily rates.
A fiscal year or financial year is a 12-month period used for calculating annual financial statements in businesses and other organizations.
In tropical and subtropical regions several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. A calendar year is an approximation of the number of days of the Earth's orbital period as counted in a given calendar.
The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; see below.
Historically, lunisolar calendars intercalated entire leap months on an observational basis.