Other forms: compound interests
Compound interest is money that's earned not just on an initial investment, but also on the interest it earns.
Interest is the money you earn when you save or invest. If you put $1000 in an account with an interest rate of 10 percent, you'll end up with $1100. With compound interest, you also earn interest on the interest itself; after another year you'll earn another $100 on your original investment, plus $10 on the first year's interest. The more time goes by, the more this amount grows, or compounds.