The Hebrew calendar’s traditional 19-year cycle with seven leap years is called the Metonic cycle.
The cycle keeps lunar months aligned with the solar seasons by adding an extra month in seven of its 19 years. In the Hebrew calendar, the added month is an additional Adar, commonly called Adar II. This arrangement allows festivals such as Passover to remain in their intended seasons rather than shifting through the solar year like purely lunar observances.
The cycle is named after Meton of Athens, who described a comparable 19-year relationship between lunar and solar cycles in the fifth century BCE. The fixed Hebrew calendar also uses detailed calculations for months and postponements, so its operation is more complex than simply inserting a month on a repeating schedule. Jewish leap years are years 3, 6, 8, 11, 14, 17, and 19 of the cycle.