A co-signer is an individual who signs a mortgage loan alongside the primary borrower, taking on equal responsibility for the loan. The co-signer's role is to:

1. Provide additional creditworthiness: A co-signer with a good credit score can help the primary borrower qualify for a mortgage or obtain a better interest rate.

2. Share loan responsibility: Co-signers are legally obligated to repay the loan if the primary borrower defaults.

3. Increase loan limits: With a co-signer, borrowers may be able to qualify for a larger loan amount.

Co-signers are often used when the primary borrower has:

- Limited credit history

- Poor credit

- Insufficient income

- High debt-to-income ratio

Co-signers can be parents, relatives, or friends who have a stable financial situation and good credit. It's important for co-signers to understand their responsibilities and potential risks before signing a mortgage loan.