A credit score condenses your borrowing track record into a single figure. In India the CIBIL, Experian and Equifax scores run from 300 to 900; in other countries the scales differ, but the idea is the same.
Five things drive it: payment history (the biggest factor), credit utilisation, length of history, credit mix and recent applications. Missing payments or maxing out cards pulls the score down; consistent on-time payments push it up.
For example, two people may earn the same salary, but the one with a 780 score gets a home loan approved faster and at a lower rate than the one at 650. It is one of the most valuable numbers in your financial life. See CIBIL score for the Indian version.