Wiktionary
n. (context logic English) A semantics for dealing with irreferential singular terms and vagueness.
Wikipedia
Supervaluationism, in logic, is a semantics for dealing with irreferential singular terms and vagueness. It allows one to apply the tautologies of propositional logic in cases where truth values are undefined.
According to supervaluationism, a proposition can have a definite truth value even when its components do not. The proposition " Pegasus likes licorice", for example, has no truth value because the name "Pegasus" fails to refer; there is nothing in the myth that would justify an assignment of any truth value. The statement "Pegasus likes licorice or Pegasus doesn't like licorice", however, is an instance of the valid schema p ∨ ¬p" ("p or not-p"), so, according to supervaluationism, it should be true regardless of whether or not its disjuncts have a truth value; that is, it should be true in all interpretations. If, in general, something is true in all precisifications, supervaluationism describes it as "supertrue", while something false in all precisifications is described as "superfalse".