Year "year", originally 秂, an ideographic compound of a person carrying a bundle of wheat denoting "harvest". Slavic besides "godŭ" "time period; year" uses "lěto" "summer; year". In the International System of Quantities (ISO 80000-3), the year (symbol, "a") is defined as either 365 days or 366 days. No astronomical year has an integer number of days or lunar months, so any calendar that follows an astronomical year must have a system of intercalation such as leap years. 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
Bissextus ecclesiastical calendars, the intercalary day is added for convenience at the end of the month of February, as February 29, and years in which February has twenty-nine days are called "bissextile," or leap years. Bissextus Bissext, or bissextus (Lat. "bis", twice; "sextus", sixth) is the day which is added to the Gregorian calendar every fourth year (except those evenly divisible by 100, unless they are divisible by 400) to compensate for the six-hour difference in length between the common 365-day year and the actual length of the solar year. Originally, the day was inserted after the 24th of February, i.e.