When December comes, the streets are filled with Christmas decorations.
His birthday is December 25th.
twelfth month of the lunar calendar
Refers to the twelfth month in the traditional Japanese lunar calendar, roughly corresponding to January in the modern calendar. Rare in everyday use; mainly encountered in historical or cultural contexts.
The twelfth month of the old lunar calendar corresponds to around January now.
It's already December now.
My younger brother was born in December.
Please submit the documents by the end of December.