Description logic (DL) is a family of formal knowledge representation languages that are used to represent and reason about structured knowledge, such as ontologies and taxonomies. Description logic is a subfield of artificial intelligence and logic, and is closely related to other logical systems such as modal logic and first-order logic.

DL is used in various applications, such as ontology engineering, semantic web technologies, and natural language processing. It is also used as a basis for other formalisms, such as OWL (Web Ontology Language), which is a popular language for representing and sharing ontologies on the web.

DL is based on a set of primitives, such as concepts and roles, that can be used to describe the properties of individuals and the relationships between them. These primitives are organized into a hierarchical structure, similar to a taxonomy, where more specific concepts are defined in terms of more general concepts. For example, the concept of "dog" may be defined as a subtype of the more general concept "animal".

DL also provides a rich set of inference rules and algorithms for reasoning about the properties of individuals and the relationships between them. For example, given a set of assertions about the properties of individuals and their relationships, DL can be used to infer new facts and detect inconsistencies in the knowledge base.