Considered the holiest day of the Jewish year, Yom Kippur is the day when Jews reflect on the past year and atone for their sins.

The Day of Atonement begins at sundown on Sept. 13 and continues until nightfall on Sept. 14, or 10 Tishrei 5774, according to the Hebrew calendar. Synagogue attendance peaks during the High Holiday, when Jews seek forgiveness for sins committed between man and God and make a pledge to avoid repeating the same mistakes in the new year.

For those who are unfamiliar with the important Jewish holiday, below are five answers to common questions surrounding Yom Kippur:

1. What does Yom Kippur mean?

Yom Kippur literally means “Day of Atonement.” It is a day devoted to “afflict the soul,” repent and reflect on sins committed in the past year. It marks the end of the 10 Days of Awe that began on the Jewish New Year or Rosh Hashanah -- a period of serious introspection.

Yom Kippur is outlined in Leviticus 16:30, which reads, “For on this day He will forgive you, to purify you, that you be cleansed from all your sins before God.”

2. What do you say?

A customary greeting on Yom Kippur includes wishing individuals an “easy fast,” Gmar Chatimah Tovah (may you be sealed in the Book of Life for a good year) and L’Shanah Tovah (for a good year) in Hebrew.

3. Why fast?

Fasting is one of three essential components of Yom Kippur. The practice comes from Leviticus 23:27 that describes "afflicting your souls," which is interpreted as abstaining from the body’s main needs, including food and drink. It is seen as an “an expression of pure faith in God.”

Jews fast for 25 hours beginning before sunset on the evening before Yom Kippur and ending after nightfall on the day of Yom Kippur. Food and drink are prohibited, but children under 13 and people who are ill or pregnant do not have to fast.

4. Are there other customs?

Jews mark the sacred and solemn day in multiple ways. The day is characterized by fasting, continuous prayer and repentance. The Talmud, a collection of rabbinical law, also outlines other restrictions including refraining from washing and bathing, putting on makeup or perfume, wearing leather shoes and having sex. Many wear white as a sign of purity and canvas shoes during the day.

5. What happens in synagogue?

Spending time in synagogue is one of the most important parts of Yom Kippur. The prayer book used on Yom Kippur, called a mahzor, means “cycle" since the calendar repeats its cycle each year.

In Orthodox synagogues, services begin around 8 or 9 a.m. and continue until about 3 p.m. Congregants usually go home and return to synagogue at 5 or 6 p.m. for the afternoon and evening services, which continue until sunset. Over the course of the day, two forms of confession are performed. The prayers, Ashamnu and Al Chet, involve asking for forgiveness from God. The former is a shorter, more general list of sins while the latter is a longer confession with a more specific list.

There are five prayer services over the course of the day:

Kol Nidrei, also known as “All Vows,” takes place on the eve of Yom Kippur. The prayer involves asking God to annul all personal vows made in the next year. While this only applies to religious vows made between man and God, over the centuries anti-Semitics saw the prayer as reason to believe Jews were untrustworthy.

While it is seen as a prayer, Kol Nidrei is technically a legal formulation designed to release individuals from promises between man and God. It is recited three times and it is the only time in the entire Jewish calendar when a tallit or prayer shawl is worn at night.

The morning prayer, Shacharit, includes a reading from Leviticus followed by Yizkor -- a memorial service for those who have lost one or both parents.

Musaf, which is held immediately after the morning service, includes a detailed account of the Yom Kippur Temple service performed in ancient times. The priests, or kohanim, who are direct descendants of Aaron from the Hebrew Bible, perform a three-fold blessing on the Jewish people. It is customary for men to cover their eyes with their prayer shawls and for women to gaze into their prayer books, since one must not look directly at the kohanim.

Minchah, or the afternoon service, includes reading the entire Book of Jonah, which emphasizes the importance of repentance and prayer.

Neilah, or the “closing of the gates,” is the final service of Yom Kippur. Symbolically, it represents the closing of the gates of heaven and God’s readiness to hear the prayers of the Jewish people. During the service the doors of the Ark containing the Torah, or the first five books of the Hebrew Bible, are opened. Neilah ends with the sounding of the shofar, or ram’s horn. The blast signals the end of the Day of Atonement and marks the time when congregants head home for the highly anticipated “breaking of the fast” meal.