Pretas and pitrs are both spirits. They are not alive but are believed to be lively enough to occasionally appear in the living world. Yama, the God of death, is the lord of both. The difference between them is that pretas are newly dead, while pitrs are long dead. Pretas are said to dance along with bhootas and pishachas when there is carnage on a battlefield. The pretas are looked down upon and are the lowest of the mythical beings.
The literal meaning of the word preta is ‘dead’ or ‘deceased’. Immediately after death, a person is supposed to become a preta. Human bodies are made up of five elements—prithvi (earth), jal (water), agni (fire), vayu (air) and akasa (space)—but preta bodies are made up of only two, vayu and akasa. Due to this, they are invisible to the human eye, but can be perceived by humans under certain conditions. Pretas are said to be extremely hungry and thirsty.
The reason for this is that they have enormous bellies and hence a huge appetite, but a limited ability to satisfy that appetite because of their extremely thin necks. They are released from this suffering and are raised to the rank and respect of pitrs once their relatives complete their funerary rituals, which last for one year after death. If the rituals are not completed, the individual—it is believed—will be stuck being a preta forever.
The pitrs continue to show interest in the affairs of their family descendants and occasionally even come down to help. For example, when Parshurama was fighting Bhishma to avenge the dishonour caused to Princess Amba, Bhishma was about to use the Praswapa weapon that would have sent Parshurama into instant sleep. Since Parshurama was not aware of the weapon, he would have surely lost the battle. Voices from the sky, however, forbade Bhishma from using the weapon on his guru.
While Bhishma desisted, Parshurama insisted on continuing the battle. Pitrs then appeared before him and stood before Parshurama’s chariot. They forbade him from fighting. This finally stopped the ferocious battle that had been going on for 23 days. The pitrs are so interested in their descendants that they are said to become hysterical when a child is born, wondering whether it will turn out good or bad.
The ritual of shraadh is prescribed for pitrs in Hinduism. It is to be performed for one’s dead father and mother on their respective death anniversaries as per the Hindu calendar and also collectively for all the pitrs during the second half of the month Bhadrapada, which is called pitr-paksha. This period is set aside for remembering one’s ancestors and hence people avoid buying new things or organising big events.