Once a year, the Jewish people are given an opportunity to reflect, pray for forgiveness and atone for their sins when the gates of the heavens are believed to be perhaps opened the widest - metaphorically speaking - and their G-d, called Hashem, is said to be the most attentive and compassionate to confessions and queries on mercy.

Once a year, Jews believe that G-d is at the pinnacle of his mercifulness, where "He will forgive you, purify you, that you be cleansed from all yours sins before G-d" (Leviticus 16:30).

This Day of Atonement in Hebrew is called Yom Kippur and on the holiday, for nearly 26 hours (according to chabad.org), the Jewish people are required to go without any food or drink, not wash their bodies or wear any form of leather, and abstain from marital relations - all in the efforts of focusing their sole attention on their relationship will G-d and asking Him to wipe their slate clean for the new year.

Going by the Jewish calendar, Yom Kippur begins several minutes before sunset on Tishrei 9 and goes until after sunset on Tishrei 10; the holiday starts this year on Sept. 25 and ends at nightfall on Sept. 26.

Many Jews, depending on their level of religious observance, pray daily and some never pray at all except on the high holidays. However, it is a known fact in Jewish communities around the world that the opportunity to pour out your soul in prayer on Yom Kippur is not something easily passed over.

"It's a time to repent. To really realize that what you have is a blessing because it could be worse or it could all be taken away," said Jessica Askari, a modern Orthodox Jew and mother of three living in New York. "To say sorry and thank you all at the same time."

Fasting "is to force us to look within ourselves, to repent, introspection," without any other distractions (other than perhaps grumbling stomachs) Rabbi Shmuel Herzfeld, who leads the Ohev Sholom National Synagogue in Washington, D.C., told NPR.

The Huffington Post said the holiday is not meant to be "comfortable," which is true because the Jewish people are required to focus on other things than immediate comfort and pleasure.

"Yom Kippur is the most serious holiday in Judaism... [Jews] vow to make an effort to be better people going forward. What makes Yom Kippur so powerful is that on that day we are not who we are, but who we wish we could be," Eric Golub, a writer for The Washington Times, said. "The one day of fasting is to purify our bodies and souls. Yet the concept of atonement is a difficult one. It is one thing to say words that sound holy. It is another thing to mean them."

The previous Jewish holiday, Rosh Hashanah, signifies the start of the new year in the Jewish calendar and so Yom Kippur is a chance for Jews to pray and ask G-d to start their new year clean of all past wrongdoings.

Here are some highlights about the holiday, without "writing a Megillah," (one of the five books of Hebrew scriptures that is also used in a cliché for extremely long notes).

Customs done before Yom Kippur begins include asking others for forgiveness, giving extra charity, performing kaparot - an atonement service - eating a festive pre-fast meal, and lighting both memorial candles and holiday candles. These are all done before the designated time that the holiday starts and the fast officially begins.

Out of the five prayer services held over the course of Yom Kippur, some of the most important prayers are the following: "Kol Nidrei," read on the eve of the holiday, Torah readings from Leviticus and the Book of Jonah, the "Al Chet" confession of sins and "Neilah," the "closing of the gates" service done at the end of the holiday.

The holiday ends with a single and long blast of the shofar, a trumpet -like instrument made out of a ram's horn that is blow by a congregation or synagogue leader. The significance of the sound is believed to be importance for many reasons, one being that it should increase and arouse a Jewish person's fear and awe in G-d, and compel the person to pray even harder. Chabad.org lists 10 reasons believed to behind the blowing of the shofar.

After the shofar is blown, the Jewish custom is to sing a song which title translates into "To The Next Year in Jerusalem." When the holiday is over, many hold a festive after-meal fast, consisting of light foods or sweet items, to symbolize a sweet start to the new year.

In simplest terms, Yom Kippur is a personal "cleansing day" for Jews around the world, where they pray for G-d to basically leave the past in the past and help them start off fresh almost as a new being coming in their homes, lives and any endeavor they continue or start to pursue.

The next Jewish holiday is Sukkot, starting this year on Sept. 30 in the evening.