- Date: 14th century
- 1 a : a time characterized by a particular circumstance or feature <in a season of religious awakening — F. A. Christie>
- b : a suitable or natural time or occasion <when my season comes to sit on David's throne — John Milton>
- c : an indefinite period of time : while <sent home again to her father for a season — Francis Hackett>
- 2 a : a period of the year characterized by or associated with a particular activity or phenomenon <hay fever season>: as (1) : a period associated with some phase or activity of agriculture (as growth or harvesting) (2) : a period in which an animal engages in some activity (as migrating or mating); also : estrus, heat (3) : the period normally characterized by a particular kind of weather <a long rainy season> (4) : a period marked by special activity especially in some field <tourist season> <hunting season> (5) : a period in which a place is most frequented
- b : one of the four quarters into which the year is commonly divided
- c : the time of a major holiday
- 3 : year <a boy of seven seasons>
- 4 [Middle English sesoun, from sesounen to season] : seasoning
- 5 : the schedule of official games played or to be played by a sports team during a playing season <got through the season undefeated>
- 6 : off-season <closed for the season>
Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to go into hibernation or to migrate, and plants to be dormant.
During May, June and July, the northern hemisphere is exposed to more direct sunlight because the hemisphere faces the sun. The same is true of the southern hemisphere in November, December and January. It is the tilt of the Earth that causes the Sun to be higher in the sky during the summer months which increases the solar flux. However, due to seasonal lag, June, July and August are the hottest months in the northern hemisphere and December, January and February are the hottest months in the southern hemisphere.
In temperate and subpolar regions generally four calendar based seasons are recognized: spring (adj. vernal), summer (adj. estival), autumn (adj. autumnal), and winter (adj. hibernal). However, ecologists in Europe and Australia are increasingly using a six season model for temperate climate regions that includes pre-spring (adj. prevernal) and late summer (adj. seritonal) as distinct seasons along with the traditional four.
In some tropical and subtropical regions it is more common to speak of the rainy (or wet, or monsoon) season versus the dry season, because the amount of precipitation may vary more dramatically than the average temperature. For example, in Nicaragua, the dry season is called Summer (Oct to May) and the rainy season is called Winter (Apr to Nov) even though it is located in the northern hemisphere.
In other tropical areas a three-way division into hot, rainy and cool season is used.