three-valued logic
[ˈθri:ˈvælju:d ˈlɔdʒik]
In logic, a three-valued logic (also trivalent, ternary, trinary logic, or trilean, sometimes abbreviated 3VL) is any of several many-valued logic systems in which there are three truth values indicating true, false and some indeterminate third value. This is contrasted with the more commonly known bivalent logics (such as classical sentential or boolean logic) which provide only for true and false.