A guarantor is a person who promises to be responsible for another person's debt or obligation if that person fails to meet their responsibilities. In other words, a guarantor acts as a backup or security in case of any default by the primary borrower or obligator. The term "guarantor" is commonly used in situations such as loan agreements, leases, and contracts where one party wants assurance that another party will fulfill their end of the agreement. A guarantor provides this assurance by taking on financial responsibility for the debt or obligation if necessary.