How long does it take for the Earth to circle the sun?
The Earth's orbital period around the Sun is called a year. There are however different definitions of a year, all of which are slightly different.
The calendar or Gregorian average year is 365.2425 days long. This is the definition of a year which most people use. Most years are 365 days long. Every 4th year, a leap year, is 366 days long. Centuries are only leap years if the year is divisible by 400 . The year 2000 was a leap year, 1900 was not.
The Julian year is exactly 365.25 days long and is used for astronomical calculations.
The tropical year is 356.24219 days long and is the time between two successive Vernal Equinoxes. The Tropical year is slightly shorter than other year definitions due to the precession of the equinoxes.
The anomalistic year is 365.259636 days long and is the time between two successive perihelions. The anomalistic year actually varies by a few days due to perturbations in the Earth's orbits due to the gravitational pull of other planets. The anomalistic year is slightly longer than other year definitions due to then precession of perihelion.
The sidereal year is 365.256363 days long and is the time for the Earth to complete an orbit with respect to fixed stars.