Adjective
trivariate (not comparable)
(mathematics) Having or involving exactly three variables.
Again, so that the set of objects under consideration be closed under subtraction, a study of trivariate polynomials usually allows bivariate polynomials, and so on. Source: Internet
It is possible to further classify multivariate polynomials as bivariate, trivariate, and so on, according to the maximum number of indeterminates allowed. Source: Internet