Debts
Informal money owed between people.

Money lent to friends and borrowed from them — no contract, no schedule, but a balance worth remembering.
Two directions
Every entry has a direction: someone owes me or I owe someone. The balance is worked out per person, so you see one number instead of a list of individual loans.
Partial repayments
A debt can be paid off in pieces. Each repayment is recorded with a date and the balance goes down. The entry leaves the open list only once it is settled in full.
Why this is separate from loans
A loan has a schedule, an interest rate and a deadline. Money owed between people usually has none of those, and forcing them would turn a simple note into a form nobody fills in.