First-order formulae which are true under any interpretation are known as valid formulae.
I am curious to know if there is a name given to those formulae which are true under any domain of discourse, but whose truth is dependent on its component predicates. For instance, consider the predicates:
$D(x) =$ '$x$ is a dog'
$M(x) =$ '$x$ is a mammal'
The formula $\forall x(D(x) \to M(x))$ would be an example of such a formula, because it is true under any domain of discourse, but only because of the choice of the predicates D and M, so it's certainly not a valid formula.