A "defining moment" is a term used to describe a crucial point in someone's life or an event that has a significant impact on their future. There are different synonyms for the phrase, such as turning point, pivotal moment, critical moment, key event, crucial stage, watershed moment, and life-changing experience. Each of these words and phrases conveys the same idea of a moment that has the power to change the course of someone's life. Whether it's a positive or negative experience, a defining moment can shape an individual's character and influence their decisions for years to come.