What we call a year is measured from equinox to equinox and known as the tropical year. It is 365.242189 days long. Our Gregorian calendar averages 365.365.2425 days so our calendar will drift over time. The sidereal year (fixed star to fixed star) is 365.256363 days. The year can also be measured by the Earth's perihelion. The perihelion to perihelion year is called the anomalistic year and is 365.259636 days.
@evilscientistca we should just come together as a planet and set a single time zone and calendar system and then have the extra .256363 at the end of each year be a global work-free holiday to get rid of leap years.
@mu Though we would have to use the tropical year as that is the one the seasons follow. ;) If you wait long enough the Gregorian calendar skips a leap year every 400 years to come close to the tropical year.