Interest, in the banking sense, is best described as:

1. Statements such as interest at 9 per cent per annum on a fixed deposit are familiar from any bank. 2. Interest is the extra money paid by institutions like banks or post offices on money deposited with them. 3. It also runs the other way: interest is paid by people when they borrow money. 4. So interest attaches to the sum involved, not to the account itself. 5. Account fees, taxes and minimum balances are separate charges and are not interest. _Source: syllabus Maths, Ch 7 'Comparing Quantities', S7.4 Compound Interest_