Interest is the amount of money that is charged on debts or given to savers to encourage them to save money.
The original form of usury was simply to loan gold or silver and charge interest on that loan. It was generally always distrusted and despised.
Today, interest rates are the norm. They are raised or lowered to encourage saving or borrowing respectively. Interest rates are used as a mechanism to control inflation.
High interest rates hit people with outstanding debts as they incur extra charges. Borrowers can go bankrupt, homes are repossessed, and businesses are ruined which can lead to mass unemployment and an economic recession.