In mathematics, computer science and linguistics, a formal language is one that has a particular set of symbols, and whose expressions are made according to a particular set of rules. The symbol \displaystyle{ \mathcal{L} } is often used as a variable for formal languages in logic.

Unlike natural languages, the symbols and formulas in formal languages are syntactically and semantically related to one another in a precise way. As a result, formal languages are completely (or almost completely) void of ambiguity.