1. A subsidence of symptoms. 2. A relapse; a return of symptoms. 3. Any retrograde movement or action. 4. A return to a more primitive mode of behavior due to an inability to function adequately at a more adult level. 5. An unconscious defense mechanism by which there occurs a return to earlier patterns of adaptation. 6. The distribution of one random variable given particular values of other variables relevant to it (a formula for the distribution of weight as a function of height and chest circumference). The method was formulated by Galton in his study of quantitative genetics.