Literally 'nine nights', this nine-day period from the new moon day to the ninth day of Ashvin is considered the most auspicious time of the Hindu calendar and is hence the most celebrated time of the year. Although it has different names in different parts of India, Hindus from all regions celebrate it. From Kashmir in the north to Tamil Nadu in the south, and from Gujarat in the west to Sikkim in the east, it is celebrated with great enthusiasm as the conquest of good over evil. Every region has its own myths and reasons to explain this.

The nine different aspects of Devi are worshipped over the nine days. These are the most popular forms under which she is worshipped: Durga: goddess beyond reach; Bhadrakali the auspicious power of time; Amba or Jagdamba: mother of the world; Annapurna: giver of food and plenty; Sarvamangala: auspicious goddess; Bhairavi: terrible, fearful, power of death; Chandika or Chandi: violent, wrathful, furious; Lalita: playful; and Bhavani: giver of existence.

The festivities culminate on the tenth day, called variously Vijayadashmi, Dussehra or Dassain when people in most parts of the country burn effigies of Ravana, Meghanatha and Kumbhakarna. In the South, on the tenth day, new ventures are undertaken and new beginnings are enforced and encouraged because it is believed that success is guaranteed. The nine-day period from the first to the ninth day in the bright fortnight of the month of Chaitra is also known as Navaratri and is dedicated to the worship of nine different aspects of Devi. These nine days are however, popular in north India only. The ninth day in this month is also celebrated as Ramanavami.

During Navaratri some people fast on all days taking only fruit and milk dishes and some fast only on the eighth or ninth day. As the festival is dear to the mother goddess, on the eighth or ninth day many people invite over nine young girls from the neighborhood. These girls are treated as the goddess herself. People ceremonially wash their feet, worship them and then offer food to the "girl goddesses".

On the first day of the Navaratri, grains of barley are planted in the puja room of the house. A small bed of mud is prepared in which barley seeds are sown after a small puja has been performed. Every day some water is sprinkled on it. On the tenth day, the shoots are about 3 - 5 inches in length. After the puja, these seedlings are pulled out and given to devotees as a blessing from god. The seedlings are placed on their caps, behind their ears, and inside books to bring good luck. This custom suggests a link to harvesting. The sowing and reaping of barley is symbolic of the "first fruit”. Soon after this festival, the sugarcane crop is harvested and the winter crops are sown.

According to one hypothesis, in ancient times, this was a festival intended for the Kshatriyas. After the four-month long monsoon when military activity was not possible, this was considered a good time to start afresh on one's conquests.

For nine days before starting on the war journey, kings prayed to the nine different aspects of Devi or Adishakti. They also prayed for their arms and ammunition. The tenth day was when the journey for the conquest began. The origin of this custom can also be traced to the Ramayana. According to it, Rama had to pray to the nine different aspects of Devi to be able to kill Ravana. He then accumulated enough power to kill Ravana on the tenth day, which was called Vijayadashmi or Victory Day. Since then, the tradition of praying to Devi for nine days has continued and was especially pronounced amongst the Kshatriyas who believed that by doing so, they too would be able to defeat the most powerful enemy.

With the change in social order and the establishment of democracy, the original significance of this festival is lost. Today, it is celebrated more for its mythological significance and reaffirms the Hindu faith in the triumph of good. Even today, the nine different forms of the goddess are worshipped. Though several communities of Hindus are staunch vegetarians, Navaratri is one exception. On the eighth day, many communities, especially Gurkhas and other hill tribes who are believers in the Devi cult sacrifice an animal. This blood sacrifice is a form of thanksgiving to the goddess for a wish that has been granted. People often sacrifice a buffalo symbolic of the killing of Mahishasura by Durga.

In Bengal, this period is celebrated as Durga Puja. In Gujarat, this is the time for the joyous Garba and Dandia dances and people pour out at night to participate in this community festival. Women and girls in all their fineries dance around the garba pot, clapping their hands in rhythmic movement. The pot is decorated with flowers, betel leaves, and has its mouth covered with a coconut. In Tamil Nadu, the first three days of the festival are dedicated to Lakshmi, the next three to Durga and the last three to Saraswati.
(explanation courtesy of webonautics.com )