Navaratri is a Hindu festival that spans over nine nights (and ten days) and is celebrated every year in the autumn season
It is observed for different reasons and celebrated differently in various parts of the Hindu Indian cultural sphere
Theoretically, there are four seasonal Navaratri
However, in practice, it is the post-monsoon autumn festival called Sharada Navaratri which is the most observed in honour of the divine feminine Devi (Durga)
The festival is celebrated in the bright half of the Hindu calendar month Ashvin, which typically falls in the Gregorian months of September and October