A credit score is a number calculated based on your credit history to give lenders a simpler "lend/don't lend" answer for people who are applying for credit or loans. This number helps the lender identify the level of risk they may be taking if they lend to someone. Lenders can also predict how likely you will repay a loan and make payments on time. It's the credit score that makes it possible to be approved instantly for credit cards at places like electronics stores and department stores.
Although there are several scoring methods, the score most commonly used by lenders is known as a FICO because of its origins with Fair Isaac and Company. Fair Isaac is an independent company that came up with the scoring method and software used by banks and lenders, insurers and other businesses. Each of the three major credit bureaus Equifax, Experian, and TransUnion worked with Fair Isaac in the early 1980's to come up with the scoring method.
The three national credit bureaus each have their own version of the FICO score with their own names, but is based on the original Fair Isaac FICO scoring method. Equifax has the Beacon system, TransUnion has the Empirica system, and Experian has the Experian/Fair Isaac system.