APA Dictionary of Psychology

n. a variable that exhibits covariation with a measured outcome or dependent variable: It is often included in an analysis so that its effect may be taken into account when interpreting the effects of the independent variables of interest. For example, covariates are used in analyses of covariance to statistically adjust groups so that they are equivalent with regard to these variables; they may also be used in multiple regression to minimize error that may arise from omitting any noncentral but potentially influential variables. Also called concomitant variable.