 Given a logic \(\bL\), a logical matrix \(\langle \bA, D \rangle\) is said to be a model of \(\bL\) if wherever \(\Gamma \vdash_{\bL } \phi\), then every valuation \(v\) on \(\bA\) that maps the elements of \(\Gamma\) to some designated value (i.e., an element of \(D)\) also maps \(\phi\) to a designated value. When \(\langle \bA, D \rangle\) is a model of \(\bL\) it is said that \(D\) is an \(\bL\)-filter of the algebra \(\bA\). The set of \(\bL\)-filters of an algebra \(\bA\) plays a crucial role in the theory of the algebraization of logic systems. We will come to this point later.