That's right, talking calculus. It is used to calculate, of course. But students of chemistry, biology, economics or government, as well as doctors, options traders and secretaries of defense, all read, hear and talk calculus. Mathematics in general is a language, with an alphabet, a vocabulary, a grammar.
Every equation is a sentence.
Mathematics is used in the writing of weather reports, great theories of the universe, State of the Union addresses and the side panels on Cheerios boxes. There are dialects of mathematics. There is mathematical slang. Mathematics borrows from other languages and they in turn borrow from mathematics. You might argue that real languages evolve over time, that they aren't invented.