Definition from Wikipedia.org:
A credit score is a numerical expression based on a statistical analysis of a person’s credit files, to represent the creditworthiness of that person, which is the likelihood that the person will pay his or her debts. A credit score is primarily based on credit report information, typically sourced from credit bureaus / credit reference agencies. Other countries might have similar scores.
Lenders, such as banks and credit card companies, use credit scores to evaluate the potential risk posed by lending money to consumers and to mitigate losses due to bad debt. Lenders use credit scores to determine who qualifies for a loan, at what interest rate, and what credit limits. The use of credit or identity scoring prior to authorizing access or granting credit is an implementation of a trusted system.