Year
a solar year, also called tropical year, is based on the seasons.  The Gregorian calendar is based on a tropical year of 365.2425 days.  This is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice.  The word "tropical" in this sense comes from the Greek tropikos meaning "turn".