The dark fortnight which falls in the Hindu calendar month of Bhadrapad (September) is known as Pitr-Paksha or Mahalay Paksha all over the Hindu World. This period is regarded to be an ideal ocassion to perform rites for the deceased ancestors to keep their spirit gratified for years.
It is a traditional religious belief that deceased ancestors from Lord Yamaraja's region visit their homes on earth during this time. So, if the rite of shraddha is performed on one of the days in the fortnight, then the subtle bodies of ancestors is considered to remain gratified for years.
Pitru Paksha reminds us of our subtle existence and requirement of our subtle or spiritual needs in the form of rites like shraddha to ensure a smooth passage from physical existence to the subtle planes.By focussing solely on gross sciences, many of these subtle measures are not practiced, even forgotten in western countries.
Funeral rites and Shraddha are different.While funeral rites are considered inauspicious, Shraddha is auspicious and gratifying.
Pitrapaksha gives a chance to repay debt to our deceased ancestors by gratifying their spirits. As such, Shraddha is a "debt of the dead"or "ceremonies of the dead" which should be performed, assuming that the dead ones are alive amongst us. The Lord of death, Yamaraja enables the dead ones to come to earth and receive offers from the descendants.This practice is made to the dead petras and pitras.
It is believed that one owes three main debts, first to Devarina(Debt to the gods ), Rishirina (Debt to the Guru) and Petranina (Debt to the forefathers).While most people prefer to perform Shraddhas' at their homes, the most devout perform Shraddha at the designated holy place.
Only after the Shraddha, he/she attains a position among the Petris or Divine Fathers in their blissful abode called Pitri-loka. Generally, considered most desirable and efficacious when Shraddha is performed by a son. Ritual of Shraddha should be performed for one's grandfather, father on the paternal side and the mother etc on the maternal side. Names of all livinzg poersons should not be associated with the rituals.