What is a Year ?

Source: en.wikipedia.org

" A year or annum is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. (...)
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 calendar, 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. 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. In English, the abbreviations "y" and "yr" are commonly used ("a" is also used) for the unit of time, though its exact duration may be inconsistent. (...) "