day of the Ox
Refers to a day in the traditional calendar marked by the zodiac sign of the Ox. Most commonly associated with the midsummer Doyo no Ushi no Hi (eel-eating day), but also occurs in midwinter.
See also: 土用の丑の日
There is a custom of eating eel on the midsummer day of the Ox.
今年の冬の丑の日はいつですか。
When is the winter day of the Ox this year?