Definition:
When a loan is taken out, it is sometimes the case that the borrower's credit and/or collateral are insufficient for the lender to justify the risk of issuing the loan, so in those cases it is sometimes possible for someone else to volunteer to be held legally liable for the debt along with the actual borrower. This person "co-signs" the loan, essentially putting their credit to work for the borrower in the faith that the borrower will repay the debt or, in the event of default, the co-signer is also held responsible.
