An intercalary month is an additional month added to a calendar to synchronize it with the solar year or lunar cycles. This adjustment helps to keep the calendar in alignment with the seasons or the phases of the moon. Different cultures have used intercalary months throughout history, such as the ancient Roman calendar, which included an extra month called Mercedonius. In the Hebrew calendar, an intercalary month called Adar II is added in leap years to ensure that the lunar calendar remains in sync with the solar year. This practice is essential for maintaining the timing of religious festivals and agricultural activities, which depend on seasonal changes.