A credit bureau is a company that collects the borrowing and repayment record of every borrower from all lenders, and sells that record back to lenders as a credit report and a credit score. In India, credit bureaus are officially called credit information companies (CICs). They are licensed by the Reserve Bank of India (RBI), and there are four of them. TransUnion CIBIL, Experian and Equifax are three of them. When most Indians say "credit score", they mean the CIBIL score.
Here is how the record is built. Every bank and NBFC reports each of its loans and credit cards to the bureaus at regular intervals, now every two weeks. Each report says how much the borrower owes and whether each payment was on time. The bureau combines the reports from all lenders into one file for each person. It identifies each person mainly by PAN, along with name, date of birth and address.
When you apply for a loan, the lender asks the bureau for your file. The bureau returns two things. The credit report lists every loan and card you have had, with its payment history. The credit score is a number that sums up how likely you are to repay. For CIBIL, it runs from 300 to 900. The lender's credit decision engine uses both to decide.
Consider a car mechanic in Ranchi with two loans: a loan for his motorcycle and a ₹30,000 loan for a phone. Eight months ago, he paid one EMI on the phone loan 45 days late. His credit report will show that late payment for several years, although its effect on his score becomes smaller with time. He can see his own score in a credit score monitoring app. Every Indian can also get one free full credit report a year from each bureau.
Bureaus sell more than reports. They sell fraud checks and analytics to lenders, built from the same data. For businesses, the same kind of record is kept by a commercial credit bureau.
A lender checks the bureau before almost every loan, from an instant personal loan app to buy now, pay later. A credit bureau is not the same as a credit rating agency. A credit rating agency grades companies and the bonds they issue, not individual people.