Rosh Chodesh is the first day of each month. The Torah instituted that each new month be commemorated with a sacrifice. While no animals are currently sacrificed, many mark Rosh Chodesh with extra singing and prayers. In some communities, women take it as a special day to gather and refrain from work in honor of the womens' refusal to contribute to the Golden Calf.
Yom Kippur, the Jewish Day of Atonement (known also as the Sabbath of Sabbaths) is considered by many to be the holiest day of the year. It is a day spent fasting and praying for God's forgiveness at the start of the new year.
Sukkot is a weeklong harvest holiday marked in autumn by the building of temporary booths outside homes in which people eat their meals and sometimes even sleep. The booths are reminders of the transiency of life and the sheltering presence of God.
Simchat Torah is a joyous festival celebrating the completion of the year's cycle of reading the Torah. It is common to find people singing and dancing in synagogues and even in the streets with Torah scrolls.
Chanukah is an eight day winter holiday commemorating a Jewish victory over Greek conquerors in the second century BCE. It is widely known as the "Festival of Lights" due to the practice of lighting a candle or oil lamp for every day of the holiday. This ritual recalls the miracle in which the oil of the Temple lights lasted for eight nights - when it was expected to last for only one night.
Passover, or Pesach, is a week long springtime festival commemorating the Exodus from Egypt. It also celebrates national redemption, and freedom from slavery. It is observed through avoidance of certain foods (especially grains) and ritual dinners called Seders where attendees retell the story of the Exodus.
Shavuot is a holiday celebrating two things: the harvest and the day the Israelites received the Torah. Many stay up all night learning to honor the latter. It is traditional to chant the Book of Ruth - and to indulge in dairy foods.
Tisha B'Av, or the 9th of Av, is a 25 hour fast that usually falls July or August. Marked by the abstention from food, drink, washing, sexual relations, and wearing leather, it is a day of lamentation for the loss of the First and Second Temples in Jerusalem.
There are assorted fast days scattered across the Jewish calendar. During the two major fast days, Yom Kippur and Tisha B'Av, one abstains from food, drink, washing, and sexual relations for 25 hours. During the other, minor fast days, one abstains from food and drink from sunup to sundown.
The High Holidays refer to the Jewish New Year (Rosh HaShanah) and the Day of Atonement (Yom Kippur) that follows 10 days later. These days may be used as a time for repentance, introspection, prayer, and good deeds.
Lag BaOmer ("the 33rd day of the Omer") is a day of celebration during the otherwise solemn period of the 49 days between the holidays of Passover and Shavuot. Many mark this day with outdoor parties and bonfires.
There are four New Years in Jewish tradition: the New Year for governments and festivals in the spring, the New Year for tithing animals in late summer, the New Year for calendars and spiritual renewal (Rosh Hashanah) in the fall, and the New Year for trees and planting in the end of winter.
Rabbinic holidays refer to those holidays that are not commanded or mentioned mentioned in the Bible but were decreed by the Rabbis during the Talmudic period (around the first six centuries of the first millenium CE).
Sefirat Ha'Omer (literally, "the counting of the Omer") is the period of 49 days between Passover and Shavuot. Each day is verbally counted off. Traditionally this period of time is a solemn one and many avoid celebrations during the count.
Tsom Gedaliah ("the Fast of Gedaliah") is a minor fast day between Rosh HaShanah and Yom Kippur, observed from dawn to nightfall, commemorating the assasination of a Judean official (Gedaliah) by fellow Judeans - an act that led to further dispersal during the Babylonian Exile.
Yom HaAtzmaut is Israel's Independence Day, celebrated on the fifth day of Iyyar (usually in April or May), marking the date when the Israeli provisional government signed their Declaration of Independence.