A lunar year is approximately 354 days long. It consists of 12 cycles of a complete lunar phase, or a synodic month, which is about 29 days.
The duration of a lunar month changes from cycle to cycle due to the oblong orbit of the moon around the Earth and the Earth around the sun. They change by a matter of hours rather than days, subsequently altering the length of every lunar year.
Several cultures and religions use a lunar calendar. The Hijri Qamari, or Islamic calendar, is a religious calendar and also the official calendar in Saudi Arabia. The Chinese, Hindu and Hebrew lunar calendars have months that match the lunar cycle, but they add intercalary months so that the overall calendars mirror a solar year.