In Laymen's Terms...
A credit score is a 3-digit rating that shows your likelihood to repay the loan you borrow in a definite length of time. Before giving out the loan, your lenders request a credit report from one of the three credit reporting agencies, such as Experian (formerly known as TRW).
This credit report reveals your personal information, financial history, and of course, how well you've managed your debts and finances in the past. Basically, it implies how wisely you have used credit in the past and how likely you'll continue to do so in the future.
Your credit score is computed based on a subset of information within your credit report, which a lending institution will use along with other factors when determining the risk factor when you apply for a credit card or request for a loan.
Although you're entitled by law to receive a free copy of your credit report annually, this free report will not reveal your actual credit score. In order to review your actual score and see where you are on the scale, you will have to pay a fee to obtain your score.