According to Jewish tradition, Rosh Hashanah is the birthday of the world. Rosh Hashanah is followed, ten days later, by Yom Kippur. Together these two days are called the High Holidays.
The holidays and the time in between them are known as the Ten Days of Repentance. The overarching theme of Yom Kippur is repentance. From the beginning to the end of the holiday, we are meant to be thinking about affecting positive change in our lives and making amends with others.
Holiday descriptions provided by Kveller.com.