In programming it is the number of arguments a function or
operator takes. In some languages functions may have
variable arity that sometimes means their last or only
argument is actually a list of arguments.
Core JavaScript 1.5 Reference:Global Objects:Function:arity arity is no longer used and has been replaced by the length property. arity is external to the function, and indicates how many arguments a function expects. By contrast, arguments.length provides the number of arguments actually passed to a function.
