The word Navaratri literally means nine nights in Sanskrit; Nava meaning Nine and Ratri meaning nights
During these nine nights and ten days, nine forms of Shakti i.e. female divinity are worshipped.
It is the nine days when we are suppose to thank the female principle of nature and the goddesses connected to them.
The first three nights are dedicated to the goddess of action and energy. Her different manifestations viz Kumari, Parvati and Kali are worshipped during these days.