It is celebrated a day before Kali Puja, the day is celebrated on the Chaturdashi Tithi of Krishna Paksha in the month of Kartik and is observed in a bid to ward off evil spirits or ghosts from their homes.
It is also known as Naraka Chaturdashi, among the Bengali community.
14 lamps, known as Choddo Pradip, are set around the house, especially in the dark corners, to chase the dark spirits away. Many also believe that the number of lamps represent the 14 forefathers.
On Bhoot Chaturdashi, it is believed that the last 14 forefathers of a family visit their living relatives on this. .
It is also a ritual to consume 14 different types of ‘saag’ or leafy vegetables (‘choddo shaak’) to mark the occasion.
At some places, ‘Aghoris’, Shaivite ascetics of the Tantric ‘kapalik’ tradition, gather on Bhoot Chaturdashi to carry out ‘puja’ and Tantric rituals.
There is also a belief, especially in rural Bengal, that tantriks were known to kidnap children the night before Kali Pujo and sacrifice them the next day to gain dark magic powers. So, it is also often believed to be a custom to keep the children safe.
Bhoot Chaturdashi is not as big a deal as Halloween, and it doesn't have all the candies. But it does have the ghosts, the fun that comes from all that's eerie, all the folklores about ghosts.