Fall, also referred to as autumn, is the season that occurs between summer and winter. In the Northern Hemisphere, it begins in September and continues through December. In the Southern Hemisphere, it begins in March and continues through June. As fall progresses to winter, the daylight hours get shorter, the temperature decreases, and the length of nighttime increases.
One of the key features of fall in temperate climates, where temperature fluctuates more throughout the year resulting in more distinct seasonal changes, is that the leaves of deciduous trees change color then fall from the trees before winter. Thus, in some regions, the changing and falling of the leaves is a clear indicator of the end of summer and the coming of winter.
Why are the seasons different around the globe?
The reason that seasons differ depending on which part of the Earth you live in is due to the rotation of the Earth about its axis, as well as its rotation about the Sun. Because the axis about which the Earth rotates is tilted relative to the plane formed by its orbit around the Sun, different parts of the planet experience different amounts of sunlight throughout the year.
During the months of May, June, and July, the Northern Hemisphere faces the Sun, so these regions get more sunlight throughout that period of time. The same is true of the Southern Hemisphere during the months of November, December, and January.
While the Northern and Southern Hemispheres experience the four seasons at different times, the tropical and subtropical regions of Earth don't really experience the four seasons at all. This is because regions around the Equator see little variation in sunlight throughout the year, so the average temperature does not vary much throughout the year, unlike regions in the Northern and Southern Hemispheres. Rather than having four seasons throughout the year, tropical regions instead have wet and dry seasons where the amount of precipitation significantly varies.
Fall vs autumn
Fall and autumn both refer to the season between summer and winter. Fall is the term that is used mostly in North America, while most of the rest of the world refers to the season as autumn. Other than that, there is no real difference. It is just a matter of preference which term is used.