Along with Yom Kippur, which holiday makes up Judaism's High Holy Days?

Along with Yom Kippur, Rosh Hashanah makes up Judaism’s High Holy Days.

Rosh Hashanah means “Head of the Year” and begins on the first day of Tishrei, the seventh month of the Hebrew calendar. It is commonly known as the Jewish New Year, although the Hebrew calendar has several different new-year observances for different purposes. Rosh Hashanah traditionally lasts two days and is marked especially by prayer and the sounding of the shofar, a ram’s horn.

The holiday begins the Ten Days of Repentance, a period of reflection that ends with Yom Kippur. In traditional imagery, Rosh Hashanah is associated with judgment and the writing of a person’s fate, while Yom Kippur is associated with repentance, atonement, and the sealing of that judgment.

A frequent mistake is to call all ten days themselves the High Holy Days. In the strictest usage, the High Holy Days are the two holidays—Rosh Hashanah and Yom Kippur. The intervening period is more precisely called the Ten Days of Repentance or Days of Awe, though broader usage sometimes overlaps.