From WordNet (r) 2.0:

quantifier
     n 1: (logic) a word (such as `some' or `all' or `no') that binds
          the variables in a logical proposition [syn: logical
          quantifier]
     2: (grammar) a word that expresses a quantity (as `fifteen' or
        `many')

From The Free On-line Dictionary of Computing (27 SEP 03):

quantifier
     
        <logic> An operator in predicate logic specifying for which
        values of a variable a formula is true.  Universally
        quantified means "for all values" (written with an inverted A,
        LaTeX \forall) and existentially quantified means "there
        exists some value" (written with a reversed E, LaTeX
        \exists).  To be unambiguous, the set to which the values of
        the variable belong should be specified, though this is often
        omitted when it is clear from the context (the "universe of
        discourse").  E.g.
     
        	Forall x . P(x)  <=>  not (Exists x . not P(x))
     
        meaning that any x (in some unspecified set) has property P
        which is equivalent to saying that there does not exist any x
        which does not have the property.
     
        If a variable is not quantified then it is a free variable.
        In logic programming this usually means that it is actually
        universally quantified.
     
        See also first order logic.
     
        (2002-05-21)