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, including the Christmas season, the first day of Þorri and the period from the middle of January to the middle of February. Since the 18th century, it has sometimes been misunderstood as synonymous with the astronomical winter solstice, which the word also can refer to in contemporary English.