Autumn (also known as fall in North American English) is one of the four temperate seasons. Autumn marks the transition from summer into winter. In the northern hemisphere, the start of autumn is generally considered to be September 21 and in the southern hemisphere, its beginning is considered to be March 21.
Around this time, deciduous trees shed their leaves. The leaves of the trees change their color to a reddish hue prior to falling. Such colored leaves have come to be colloquially called "fall foliage". In the temperate zones, autumn is the season during which most crops are harvested, and deciduous trees lose their leaves. It is also the season during which days get shorter and cooler, the nights get longer, and precipitation gradually increases (in some parts of the world).
The word 'autumn' is derived from the French word automne, and became popular in usage for the season since the 16th century. The North American name for the season, 'fall', probably derived as a contraction of the phrase "fall of the leaves", and since became used interchangeably.