Navratri, the festival of nine nights is dedicated to Goddess Durga and her nine forms. According to the Hindu calendar, Navratri begins from the first day of the bright fortnight of Ashwin which usually coincides with the end of the rainy season.
The nine days have great religious significance as Goddess Durga, the divine mother, had destroyed the evil force (in the form of the demon Mahisashura) during this period.