 The term ‘algebraic semantics’ was (and many times still is) used in the literature in a loose way. To provide a logic with an algebraic semantics was to interpret its language in a class of algebras, define a notion of satisfaction of a formula (under a valuation) in an algebra of the class and prove a soundness and completeness theorem, usually for the theorems of the logic only. Nowadays there is a precise concept of algebraic semantics for a logic system. It was introduced by Blok and Pigozzi in Blok &amp; Pigozzi 1989. In this concept we find a general way to state in mathematically precise terms what is common to the many cases of purported algebraic semantics for specific logic systems found in the literature. We expose the notion in this section. To motivate the definition we discuss several examples first, stressing the relevant properties that they share. The reader does not need to know about the classes of algebras that provide algebraic semantics we refer to in the examples. Its existence is what is important.