What does Context-Free Grammar generate?

The concept of Context-Free Grammar (CFG) is central to formal language theory in computer science. A Context-Free Grammar is specifically designed to generate Context-Free Languages (CFLs), which are important in the study of programming languages and compilers.

A Context-Free Language is characterized by its ability to be generated by a grammar where the left-hand side of every production rule consists of a single non-terminal symbol. This structure allows for more complex relationships in the generated language than simpler grammars, such as Regular Languages, which only allow production of sequences that do not require nested or recursive structures.

CFGs are particularly useful in defining the syntax of programming languages, where rules can evoke nested structures, such as balanced parentheses in expressions. Therefore, the primary function of a Context-Free Grammar is to construct languages that fit this definition, making "Context-Free languages" the correct answer in this context.

The other language classes—Regular languages, Context-sensitive languages, and Unrestricted languages—represent hierarchies in the Chomsky hierarchy, each more powerful than the last, but they do not specifically refer to the output of CFGs as Context-Free Languages do.