title: What are free variables?
body: <p>Javascript closure definition says :</p>
  
  <blockquote>
    <p>A "closure" is an expression (typically a function) that can have free
    variables together with an environment that binds those variables
    (that "closes" the expression).</p>
  </blockquote>
  
  <p>Can some one explain to me the concept of free variables ? Is this concept Javascript specific or applies to other languages also ?</p>