Winter is one of the four seasons of temperate zones. Calculated astronomically, it begins on the solstice and ends on the equinox. It is the season with the shortest days and the lowest average temperatures. It has colder weather and, especially in the higher latitudes or altitudes, snow and ice. The coldest average temperatures of the season are typically experienced in January in the Northern Hemisphere and in July in the Southern Hemisphere.

Meteorological winter is the season having the shortest days and the lowest temperatures. Night-time predominates the winter season, and in some regions it has the highest rate of precipitation as well as prolonged dampness because of permanent snow cover or high precipitation rates coupled with low temperatures, precluding evaporation. Blizzards often develop and cause many transportation delays. A rare meteorological phenomenon encountered during winter is ice fog, which is composed of ice crystals suspended in the air and happening only at very low temperatures, below about −30 °C