Guarantor

In general, the term "guarantor" refers to a party that guarantees something. So, if a quarterback says before the Super Bowl “We’re 100% definitely going to win,” he becomes the guarantor.

The word has particular meaning in real estate. It’s the co-signer who promises to pay if a tenant stiffs the landlord on rent.

You’re just out of college, trying to get a job and not really able to afford an apartment. As such, no landlord will sign a lease with you. To get you out of the house, your parents agree to become guarantors for the lease. They co-sign the lease for you, promising to pay if you flake out. If you miss a payment, they are on the hook.