A surrogate is a person or thing that takes the place of another. In a medical context, it refers to an artificial or substitute for something else, such as a surrogate mother who carries and gives birth to a child for another couple. In psychology, it refers to a person's representation of an object or concept, such as a surrogate for a lost loved one. In statistics, it refers to a variable that is used as a substitute for another, such as using height as a surrogate for genetic differences between populations.