A co-signer is a person who agrees to take responsibility for a loan or lease alongside the primary borrower. This arrangement is often used when the primary borrower has a limited credit history or a low credit score, making it difficult for them to secure financing on their own. The co-signer's creditworthiness can help the borrower obtain better loan terms or approval. If the primary borrower fails to make payments, the co-signer is legally obligated to cover the debt. This means that the co-signer's credit score may be affected if payments are missed. It’s important for both parties to understand the risks involved in this arrangement.