Description logics are a family of logics that are typically (always?) less expressive than full first-order predicate logic (FOPL), but have more efficient reasoning procedures available (e.g. the procedures are decidable).Description logics share some characteristics with frames, semantic networks, and object oriented knowledge representations. In particular, they usually take an object-centred view (rather than concentrating on relations, as in FOPL), and have some notion of a subsumption relation built-in (similar to inheritance). Thus, description logics are often used for describing the objects in some domain as a taxonomy or ontology, and are popular in the semantic web.
NEM: My knowledge of description logics is fairly basic, so there may be errors in the above.