Linked from
The 13 pages that link to Regular language, each with the reason it gives.
Regular expressionRelated: It is the exact class of languages denoted by the formal notation.
SemigroupRelated: Its syntactic semigroup encodes which word contexts distinguish its strings.
Finite automatonNarrower topic: These are exactly the languages finite automata recognize.
Chomsky hierarchyRelated: Regular languages form the smallest class in the hierarchy.