The  biblical Hebrew calendar , also known as the Jewish calendar, is a lunisolar system dating back to ancient times. It's based on the cycles of the moon and adjusted to match solar years. This calendar plays a significant role in Jewish religious and cultural life, determining important holidays and observances, such as Passover and Yom Kippur. It consists of 12 or 13 months and has been a cornerstone of Jewish timekeeping for millennia, preserving a rich historical and religious legacy.