Chanukah חנוכה
Eight days commemorating the Hasmonean victory and the jar of oil that burned for eight days.
Chanukah is a festival established by the sages rather than the Torah, and the only one about which the Talmud asks outright: «what is Chanukah?» The answer is brief: the Greeks defiled all the oil in the Temple; when the Hasmoneans won they found one sealed jar, enough for a day, and it burned for eight.
The historical side matters as much. Antiochus IV banned Shabbat, circumcision and the sanctification of the new moon and set an idol in the Temple; the revolt begun at Modiin by the priest Matityahu and his sons was both a war against an empire and a war within the nation. In 3597 the Temple was purified.
The commandment is a light for a household: Beit Shammai said to descend in number, Beit Hillel to ascend, and the law follows Hillel — «in holiness one rises».