'Shraddha' is a Sanskrit word which literally means any act that is performed with all sincerity and faith (श्रद्धा). In Hindu religion, it is the ritual that one performs to pay homage to one’s ancestors (पितर्), especially to one’s parents who are passed away. It is a way for people to express heartfelt gratitude and thanks towards their parents and ancestors, for having helped them out for what they are today and praying for their peace.
It also can be thought of as a "day of remembrance". It is performed for one’s father and mother separately, on the days they became deceased. It is performed on the death anniversary or collectively during the ‘Pitru Paksh’ (fortnight of ancestors), in autumn.
In India, the importance given to the birth of son is to ensure that there will be a male descendant to perform ‘Shraddha’ ceremony after one's death.
When human being dies, its subtle body gets freed from the dead body after performing the ritual of ‘Shraddha’ and gets position in the subtle plane, meant for soul of dead persons. From that moment onwards, it assumes the designation of ‘Pitar’.
In practice, the host (Karta) i.e. the person who performs the ‘Shraaddha’, invites Hindu Priests (‘Pundits’ / ‘Purohits’). These priests are considered to be very noble, worthy & knowledgeable. Considering these Hindu priests as his real parents, sumptuous food with all hospitality & dedication is served to them. When these Hindu priests finish their lunch, the main priest (Aacharya) performs 'Pind Puja'. Then every family member & relatives of deceased person present at home worship that 'Pind' & offer their respect by bowing down. 'Pind ' are the oval shaped balls made out of cooked rice & given as offerings to the ancestors (पितर्).
The host then distribute fees (Dakshina) to all Hindu priests.
Since this is one of the most important and noble rituals (meant to cleanse the mind and soul), Hindu sages envisaged that the performer of this ritual understands what is he doing.
Shraddha Period :
In Hindu calendar, second half of the month ‘Bhadrapada’ is called ‘Pitru Paksha’. In this particular period, out of 15 days, 'Shraddha' is performed by the host depending upon the day (tithi) of his deceased father or mother. The only exception is 14th day out of 15, on which 'Shraddha' can't be performed. 15th day is termed as ‘Sarvpitri Amavasya’ . On this day, those hosts who don't know or remember the day of demise of their parents can perform 'Shraddha'. This particular day is the chance for performing 'Shraddha' for those hosts, who have missed a particular day (tithi) of their parents to do so. On 'Sarvpitri Amavasya' day, one can perform 'Shraddha' not only for his mother or father or both but also for all those close family members who are already passed away.
At this particular time period (generally September), crops in India and Nepal are ready and the produce is offered as a mark of respect and gratitude (by way of ‘Pind ’) to the ancestors first.