Zot Chanukah (this is Chanukah) is a reference in Torah literature to the eighth day of Chanukah, since on that day the Torah reading includes the verse Zot Chanukat Ha’Mizbe’ach (this is the inauguration of the altar. Numbers 7:64).
Ashkenazi Jews used to call this day “the dedication of the altar” after the same verse.
The Maharal of Prague notes in his Book of Minhagim the custom of the Jews who lived along the Rhine river not to work on the eighth day of Chanukah. Chassidic rebbes hold a Tish on this day.
The Ari Z’l compared the first seven days of Chanukah to the first seven divine emanations out of the 13, and attributed to the eighth day the last six. The word Zot in Kabalistic tradition refers to the Shekhinah, God’s emanation on earth, as in the verse B’Zot yavo Aharaon el ha’Kodesh (With That shall Aharon come into the holy sanctuary. Leviticus 16: 3).
Chassidim believe Chanukah is a continuation of the High Holidays, and those who did not repent for their mistakes in the ten days between Rosh Hashanah and Yom Kippur still have until the eighth day of Chanukah. This is based on the verse B’Zot yechupar avon Ya’acov (With That shall the sin of Ya’akov be redeemed. Isaiah 27:9).