Jewish festivals occur on the Hebrew calendar, which is based on both the sun and moon’s cycles—vs. the Gregorian calendar, which is based solely on the sun’s. Jewish holidays encompass biblical festivals, seasonal milestones, historical celebrations, and rabbinic observations.
There are multiple terms in the Hebrew language to distinguish between holidays—Festival Days refer to the six Biblically-mandated festival dates, while High Holy Days refer to Yom Kippur and Rosh Hashanah, and the Three Pilgrimage Festivals commemorate historical Jewish migrations.
It is also important to note that Jewish “holidays” begin and end at sunset, rather than at midnight—as in the Gregorian calendar.