Homonym: interest (Curiosity)
Interest is the cost of borrowing money or the reward for saving it. When you take out a loan from a bank, you pay interest on the amount borrowed. This is how lenders earn money. Conversely, when you deposit money in a savings account, the bank pays you interest as a reward for allowing them to use your funds.
Interest is usually expressed as a percentage of the principal amount, which is the original sum of money. There are different types of interest, such as simple interest and compound interest. Simple interest is calculated only on the principal, while compound interest is calculated on the principal plus any accumulated interest.