What is the term for one who agrees to pay money or perform an act if the principal fails?

The term for one who agrees to pay money or perform an act if the principal fails is referred to as a surety. In the context of bail and surety bonds, the surety is the party that takes on the obligation to ensure that the principal — the person who has been granted bail — meets the conditions of their release. If the principal fails to appear in court or otherwise defaults on their obligations, the surety is responsible for fulfilling those obligations, which may involve paying the bail amount set by the court.

Understanding the role of the surety is crucial in the bail industry, as it establishes the relationship and liabilities among the parties involved in the bail process. This involves the surety taking a financial risk based on the principal's promise to adhere to the terms set by the court.