Questions related to formal languages, grammars, and automata theory
Formal languages are sets of strings, i.e. sequences over symbols from some alphabet.
In general, the field of formal languages studies mathematical and logical properties of and relationships between languages (or sets) of strings (or sequences of symbols) over alphabets (or sets of symbols). Commonly encountered varieties of formal languages are regular languages, context-free languages, context-sensitive languages, recursive languages, and undecidable languages.
The computability tag is better suited for question about computability and Turing machines.