title: Define "cyclic data structures"
body: <p>At the <a href="http://www.json.org/js.html" rel="noreferrer">JSON site</a> it says </p>
  
  <blockquote>
    <p>JSON does not support cyclic data
    structures, so be careful to not give
    cyclical structures to the JSON
    stringifier.</p>
  </blockquote>
  
  <p>What does it mean by this? Can someone give me an example of such a data structure in Javascript?</p>