bound variable

from The Free On-line Dictionary of Computing (8 July 2008)

bound variable

   1. A bound variable or {formal argument} in a function
   definition is replaced by the {actual argument} when the
   function is applied.  In the {lambda abstraction}

   	\ x . M

   x is the bound variable.  However, x is a {free variable} of
   the term M when M is considered on its own.  M is the {scope}
   of the binding of x.

   2. In logic a bound variable is a quantified variable.  See
   {quantifier}.