Midwinter is the middle of the winter. The term is attested in the early Germanic calendars where it was a period or a day which may have been determined by a lunisolar calendar before it was adapted into the Gregorian calendar. It appears with several meanings in later sources. In Old English, midwinter could mean Christmas Day or sometimes the Christmas season; indirectly it could also mean the winter solstice, which was regarded as 25 December. In Old Norse, miðvetr (midwinter) meant either the first day or entire period of the Scandinavian month Þorri.