Navami is the Sanskrit word for "ninth", and is the ninth day in the lunar fortnight of the Hindu calendar. Each month has two Navami days, being the ninth day of the "bright" and of the "dark" fortnights respectively. From Wikipedia
The festival marks the culmination of Chaitra Navratri with rituals, fasting, and processions, centered in Ayodhya, the birthplace of Lord Rama.
