From the Oxford Dictionary of English:
The time taken by the earth to make one revolution around the sun.
The length of the year depends on the manner of calculation. For ordinary purposes the important period is the tropical year (also called astronomical year, equinoctial year, or solar year) which is the time between successive spring or autumn equinoxes, or winter or summer solstices, roughly 365 days, 5 hours, 48 minutes, and 46 seconds in length. This period thus marks the regular cycle of the seasons.