Predatory lending is one form of abuse in the granting of loans. It usually involves granting a loan in order to put the borrower in a position that one can gain advantage over him or her. Where the moneylender is not authorised, it could be considered a loan shark.
Usury is a different form of abuse, where the lender charges excessive interest. In different time periods and cultures the acceptable interest rate has varied, from no interest at all to unlimited interest rates. Credit card companies in some countries have been accused by consumer organisations of lending at usurious interest rates and making money out of frivolous "extra charges" 
Abuses can also take place in the form of the customer abusing the lender by not repaying the loan or with an intent to defraud the lender.