Debt is what you owe - it comes in many forms, including mortgages, personal loans, credit card balances, hire purchase agreements, loans from family.
The payments due on a long-term debt consisting of interest and principal, eg. a monthly mortgage payment.
This is to do with the structure of the population and changes to that structure.
Direct debits (DDs) are a way of paying someone a variable amount direct from your bank account, usually on a fixed day of the month. Direct debits are ideal for bills that are a different amount each month – like telephone and power bills.