The main difference between yields and interest rates is that each term refers to different financial instruments. Yield commonly refers to the dividend, interest or return the investor receives from a security like a stock or bond, and is usually reported as an annual figure.
A Yield Example
For example, if PepsiCo (NYSE: PEP) pays a quarterly dividend of 50 cents and the stock price is $50, then the annual dividend yield would be 4% [(50 cents x 4 quarters) / ($50)]. Therefore, the current yield is 4%.
If the stock price increases to $100 and the dividend remains the same, then the yield becomes 2%. (Bond yield is a bit more complex; if you want to learn about it, take a look at our tutorial: Bond Basics: Yield, Price And Other Confusion.)
An Interest Rate Example
As an example of interest rates, suppose you go into your bank to borrow $1,000 for a new bicycle, and the bank quotes you a 5% interest rate on your loan. If you borrow this amount for one year, the interest you would pay on top of paying back the $1,000 would be $50 (simple interest: $1000 x 0.05).
If the interest rate is compounded, the interest rate you will pay would be a little bit more. Lenders charge interest to compensate for the opportunity cost of not being able to invest it somewhere else. (To learn more about compound interest, see Accelerating Returns With Continuous Compounding.)