Pitri Paksha...
The dark fortnight in the Hindu month of Ashwin corresponding to September-October is called Pitri Paksha. During this time Hindus offer black sesame seeds in water called Tillanjali in the name of their departed ancestors. Paarnava Sradha is performed on the lunar day on which their Pitri departed from the physical body. According to the Dharma Shastras we owe three principal debts; debts to the Devatas, debts to the Rishis and debts to the Pitras. The debt to the Pitras is the greatest of these three, the reason being that your Pitras were your visible Gods.
Parents made tremendous sacrifices for their children's welfare suffered financial, physical and mental strains to look after the welfare of their children. Hence, they are most worthy to be repaid by their offspring. The debts to the Pitris are paid through the performance of Sradhas. The meaning of Sradha is an act of devotion or that which is given in devotion to the Brahmanas in honour of the manes and is a term synonymous with paying our debts to our ancestors. Karam Kanda texts recommends that as Hindus we should perform Pinda -Daan and give charity to learned Brahmanas and also feed them. Pinda-Daan at midday is exceedingly beneficial to the Pitras because it makes them remain happy throughout the year and bless their offspring with happiness.