'Navratri' means the 'nine nights'. 'Nava' means 'nine', and 'ratri' means 'night'.
Nights provide rest and rejuvenation. At night you turn inward (you sleep) and you feel refreshed and rested in the morning. In the same way, Navratri or the Nine Nights is that time (of the year) when you turn inward towards your source. It is the time of the year to spend with yourself, nurturing and rejuvenating yourself through prayers, chants, meditation, fasting, and other spiritual practices, and coming out feeling refreshed, renewed and creative.