 An equational class of \(L\)-algebras is a class of \(L\)-algebras that is definable in a very simple way (by equations) using the \(L\)-algebraic language. An \(L\)-equation is a formula \(\phi \approx \psi\) where \(\phi\) and \(\psi\) are terms of the \(L\)-algebraic language (that is, \(L\)-formulas if we take the propositional logic's point of view) and '\(\approx\)' is the formal symbol for the equality (always to be interpreted as the identity relation). An equation \(\phi \approx \psi\) is valid in an algebra \(\bA\), or \(\bA\) is a model of \(\phi \approx \psi\), if for every valuation \(v\) on \(\bA, \bv(\phi) = \bv(\psi)\). This is exactly the same as to saying that the universal closure of \(\phi \approx \psi\) is a sentence true in \(\bA\) according to the usual semantics for first-order logic with equality. An equational class of \(L\)-algebras is a class of \(L\)-algebras which is the class of all the models of a given set of \(L\)-equations.