In statistics, a covariate is a variable that is possibly predictive of the outcome under study. A covariate may be of direct interest or it may be a confounding or interacting variable.

Why IQ is not a covariate in cognitive studies of neurodevelopmental disorders
ASSIGNMENT TO TREATMENT GROUP ON THE BASIS OF A COVARIATE
Assessment of Actual Significance Levels for Covariate Effects in NONMEM
The mistreatment of covariate interaction terms in linear model analyses of behavioural and evolutionary ecology studies
Improved tests for a random effects meta‐regression with a single covariate
Assessing Sensitivity to an Unobserved Binary Covariate in an Observational Study with Binary Outcome
Addenda and Corrigenda: Volume 2: Assignment to Treatment Group on the Basis of a Covariate
Matched Sampling for Causal Effects: Assessing Sensitivity to an Unobserved Binary Covariate in an Observational Study with Binary O...
A point process framework for relating neural spiking activity to spiking history, neural ensemble, and extrinsic covariate effects.
PSMATCH2: Stata module to perform full Mahalanobis and propensity score matching, common support graphing, and covariate imbalance t...