Noun
Chomsky hierarchy (plural Chomsky hierarchies)
(computer science, linguistics) A containment hierarchy of classes of formal grammars. From least to most specialized, the classes are: recursively enumerable, context-sensitive, context-free, and regular.
The hierarchy Set inclusions described by the Chomsky hierarchy The Chomsky hierarchy consists of the following levels: * Type-0 grammars ( unrestricted grammars ) include all formal grammars. Source: Internet