A year is the time it takes Earth to make one complete trip around the Sun: about 365 days. This journey through space gives us our seasons, as different parts of Earth tilt toward or away from the Sun during the orbit.

We organize our lives around years. You celebrate your birthday once a year. School starts in one year and ends in another. Scientists measure geological changes over millions of years, while historians mark important events by year: the Declaration of Independence in 1776, the first Moon landing in 1969.

A calendar year runs from January 1 to December 31, but other kinds of years exist too. A school year typically runs from August or September through May or June. A fiscal year is any twelve-month period a business or government uses for budgeting and accounting, which might not match the calendar year at all.

Because Earth's orbit actually takes about 365.25 days, we add an extra day every four years in February, creating a leap year with 366 days. Without leap years, our calendar would slowly drift out of sync with the seasons, and eventually summer would arrive in December.

The word also describes how old someone or something is: a ten-year-old student, a hundred-year-old oak tree, a two-year-old puppy.