Debt jubilees were a religious and state-administrative practice in premodern times where the sovereign would declare either all or sweeping categories of debt as voided. This happened primarily after wartime so that debts of dead subjects would not transfer down to their descendents and retard society's capability to recover from war. Because of the enormous impact of such debt cancellations on public prosperity, the occasion usually coincided with festivities and "jubilees".
Michael Hudson has written frequently on this subject.
The religious meaning of the term in the christian context specifically is that humanity had accumulated a debt to God through it's sins and that Jesus Christ repaid in our stead.