A PRUZBUL is a form that one fills out during the observance of the Shemittah – Sabbatical year.
Any debts that are unpaid at the conclusion of the last day of the Shemittah year are canceled. Even if a borrower wishes to repay his debt, the lender may not accept it unless he reminds the borrower that the debt has been canceled and the borrower still insists on giving him the money “as a gift.”
At the same time, the Torah forbids us to refrain from lending money for fear of Shemittah canceling the loan and commands us to lend, despite the possibility that we may not be paid back.
As the Shemittah year has, over the years, become a rabbinic law, one can circumvent this lender/borrower issue. Many have the custom to make a PRUZBUL before Rosh Hashanah immediately prior to the Shemittah year, to be able to collect payment throughout the Shemittah year. Once the PRUZBUL has been made, any additional loans will require an additional PRUZBUL.
Others make a PRUZBUL at the end of the seventh year, just before the loans are cancelled. And finally, others make the PRUZBUL twice, once before the Shemittah year, and once again just before it concludes.