Definition from Wiktionary, the free dictionary
- (programming) A variable that is not bound to a storage location.
- (mathematics, logic) A variable (occurring within some expression or well-formed formula) which is not bound by a quantifier or analogous symbol (such as a lambda abstractor, the "differential d" near the end of an integral or differential form, or a summation symbol).
Related terms 
variable that is not bound to a storage location