A year is a unit of time that typically consists of 365 days, or 366 days in a leap year. It is based on the Earth's orbit around the Sun, which takes approximately 365.25 days. To account for this extra quarter of a day, an additional day is added every four years, creating a leap year. In the Gregorian calendar, which is widely used today, a year is divided into 12 months, each varying in length from 28 to 31 days. The year begins on January 1 and ends on December 31, marking the passage of time in various cultures and societies.