A season is a part of a year. Many areas of the Earth have four seasons in a year: spring, summer, autumn (British English) or fall (US English), and winter. 

In some areas, there are a different number of seasons.  For example, the tropical parts of Australia (the northern parts of Queensland, Western Australia and the Northern Territory) have wet and dry seasons.  These are in addition to, or replace the regular season names.

In places which are tropical and subtropical, there are two seasons: the rainy (or wet, or monsoon) season and the dry season. This is because the rain changes more than the temperature.

Summer is a warm season because the days are longer and the Sun is high in the sky, giving direct light to the ground.    Winter is a cold season because the days are shorter and the Sun is low in the sky, giving indirect light to the ground.  Both the changes in the length of the day and the height of the Sun at noon are caused by the tilt of the Earth's spin axis with respect to the plane of the Earth's path around the Sun.  At any time, in any season, the northern and southern hemispheres (halves of the Earth) have opposite seasons.

Dates 
Seasons begin and end on different dates in different countries. In the United States, people say the seasons begin at the solstices and equinoxes. The summer solstice is the longest day of the year, and the winter solstice is the shortest. The equinox is the time when the day and the night are the same number of hours, assuming the sun were a point of light at its center. Since civil dawn occurs when the edge of the sun first appears over the horizon and civil dusk occurs when the edge drops over the horizon, the civil length of day is 12 hours long several days prior to the equinoxes. In the USA, summer begins at summer solstice, winter at winter solstice, spring at the spring (vernal) equinox and autumn at the autumnal equinox.

In Britain, people traditionally say that the seasons begin about seven weeks earlier: spring begins on Candlemas (February 2), summer on May Day (May 1), autumn on Lammas (August 1), and winter on All Hallows (November 1). These are near the cross-quarter days halfway between the solstices and the equinoxes. The Irish calendar is similar, but Spring begins on February 1.

In Denmark, spring begins on March 1, summer on June 1, autumn on September 1 and winter on December 1. In Australia, summer begins on December 1, autumn on March 1, winter on June 1, and spring on September 1.

In the Chinese calendar and the Northern parts of India, the solstices and equinoxes are in the middle of each season. Summer happens in the hemisphere tilted towards the sun.

High season 
High season is the time of year that people travel. During high season hotels and resorts increase their prices because demand is higher than in offseason. For example, winter is high season for skiing; summer is high season for beaches.

Related pages
 Northern Hemisphere
 Southern Hemisphere
 Eastern Hemisphere
 Western Hemisphere
 Equator
 Tropic of Cancer
 Tropic of Capricorn
 Arctic Circle
 Antarctic Circle

References

Other websites 
 Definition from Dictionary.com
 Names of seasons in various languages from Princeton University
 What causes the seasons?

 
Units of time