A season is a sub-division of the year, marked by changes in weather, ecology, and hours of daylight.

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, 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. 
• 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

• Hot regions have two or three seasons; the rainy (or wet, or monsoon) season and the dry season, and in some tropical areas, a cool or mild season
• Temperate and sub-polar regions, have generally four calendar-based seasons: spring, summer, autumn and winter. 
• However, ecologists mostly use a six season model for temperate climate regions that includes pre-spring and late summer as distinct seasons along with the traditional four.

• Estival (high summer): Begins June in most temperate climates. Trees are full of leaves. Birds hatch and raise offspring.
• Serotinal (late summer): Generally begins mid to late August. Deciduous leaves begin to change color. Young birds reach maturity and join other adult birds preparing for fall migration.
• Autumnal (fall): Generally begins mid to late September. Tree leaves in full color then turn brown and fall to the ground. Birds migrate back to wintering areas.
• Hibernal (winter): Begins December (mild temperate), November (cool temperate). Deciduous trees are bare and fallen leaves begin to decay. Migrating birds settled in winter habitats.