A co-signer is a person who agrees to be legally responsible to pay a debt if the borrower does not pay back a loan as agreed. A co-signer may be an option if you are trying to make a large purchase, such as a car, and if you are unable to qualify for the loan on your own.
If you are asked to co-sign a loan for someone, you are responsible for the debt if it isn't paid as agreed. If a lender reports to any of the three nationwide credit bureaus, the loan will be reflected on credit reports issued by those bureaus, and your credit scores may be impacted if payments aren't made on time.