In short, a good credit score is one that is high enough to get you the loan you want at the rate you want. The actual number that is considered to be a good credit score depends on the type of loan you plan to get and the institution you are working with. In general, you can get the best rates on a mortgage if your score is above 760 and the best rates on an auto loan if your score is above 720.
Even if your FICO credit score is lower, you can still get a loan, but you may have to pay a larger down payment or higher interest rate. It's a good idea to check your credit score well before you apply for a loan so that you aren't surprised if it is lower than you thought. If you plan ahead, you can take steps to improve your credit score and get a better rate.