Navratri is a nine days festival dedicated to Goddess Durga. Navratri is a Sanskrit word which literally means nine nights. During these nine nights and ten days, Goddess Durga is worshipped in 9 different forms, known as Navdurga. The tenth day is celebrated as Vijayadashami when idols of Goddess Durga are immersed into the water body.
Navratri is celebrated in most Indian states. However Navratri is very popular festival in the western states of Gujarat, Maharashtra and the southern state of Karnataka. On the very first day of Navratri, Goddess Durga is invoked into a Kalash with full Vedic rituals along with chanting of Mantras. The invocation and dwelling of Goddess Durga into the Kalash is known as Ghatasthapana or Kalashsthapana and is done at an appropriate time of the day.
In West Bengal Navratri is celebrated as Durga Puja. In West Bengal, Goddess Durga is worshipped on the last three days of Navratri and these three days are famously known as Durga Saptami, Durga Ashtami and Durga Navami. It would be correct to say that Durga Puja in West Bengal is a smaller version of 9 days Navratri. Kalparambha and Bilva Nimantran during Durga Puja, which is done on the sixth day of Navratri, is symbolically same as Ghatasthapana or Kalashsthapana in other states.
Hindu religious books suggest 7 days Navratri, 5 days Navratri, 3 days Navratri, 2 days Navratri or even 1 day Navratri as an alternative to 9 days Navratri.
Jyoti Kalash, Kumari Puja, Sandhi Puja, Navami Homa, Lalitha Vrat and Chandi Path are other famous rituals and events which are observed during 9 days Navratri.