Yom Kippur, also known as the Day of Atonement, is a major holiday in Judaism. It is the holiest day of the year and holds incredibly important significance for the Jewish people. One of the most hallmark practices of Yom Kippur is fasting - this is done to afflict the soul and assist in the ability for meaningful prayer. Jewish people also do not wear leather shoes, bathe, or apply lotion during Yom Kippur for the same reason.
Yom Kippur is usually pronounced a few different ways depending on the person: yahm kip-per, yahm ki-por, yohm kip-per, or yohm ki-por. Since Yom Kippur is not a "happy" holiday, the typical Hebrew holiday phrase "Chag Sameach" is inappropriate. Instead, Jewish people say "G'mar Chatima Tova" which translates to "may you be inscribed in the Book of Life for good". But what is the Book of Life?
After Rosh Hashanah, the Jewish New Year that comes right before Yom Kippur, Jewish people use the Day of Atonement (Yom Kippur) to pray for forgiveness and cleanse their souls in hope to be inscribed in the Book of Life. Names are said to be written by G-d during Rosh Hashanah and then sealed on Yom Kippur, the atonement practice is important for this reason. The goal is to be sealed into the Book of Life and avoid death another year.