Navratri symbolises nine avatars of the deity, which killed nine evil forces.
In Bengal, Durga Puja is celebrated for four consecutive days -- Mahasaptami, Mahashtami, Mahanavami and Vijaya Dashami, which marks the idol's immersion.
The last day of the Bengali festival is Dusshera in other parts of India. Of course, the end of Navratri sets off a number of other festivals, starting with Diwali.
Also read: Durga Puja: It's a million dollar business