Definition of 'Cosign'
The act of signing for another person's debt which involves a legal obligation made by the cosigner to make payment on the other person's debt should that person default. Having a cosigner is way for individuals with a low income or poor/limited credit history to obtain financing.
This term is also commonly spelled "co-sign".
Investopedia explains 'Cosign'
A cosigner's obligation to repay debt arises only after the borrower has defaulted on the loan; however, cosigning a loan is not without risk. A person cosigning a loan should be comfortable with the borrower's ability to repay the debt.