formal language. noun. 1. a language designed for use in situations in which natural language is unsuitable, as for example in mathematics, logic, or computer programming. The symbols and formulas of such languages stand in precisely specified syntactic and semantic relations to one another.
That's pretty much all I know.
Can a formal language express ideas which aren't trivial but can be shown to be true by virtue of just content? E.g. (I think) "this sentence is true".