Source : WordNet®

metalanguage
     n : a language that can be used to describe languages

Source : Free On-Line Dictionary of Computing

metalanguage
     
        1. [theorem proving] A language in which proofs are
        manipulated and tactics are programmed, as opposed to the
        logic itself (the "{object language}").  The first {ML} was
        the metalanguage for the Edinburgh {LCF} proof assistant.
     
        2. [logic] A language in which to discuss the truth of
        statements in another language.