title: Parallel Python: What is a callback?
body: <p>In <a href="http://www.parallelpython.com/" rel="noreferrer">Parallel Python</a> it has something in the <i>submit</i> function called a <i>callback</i> (<a href="http://www.parallelpython.com/content/view/15/30/" rel="noreferrer">documentation</a>) however it doesn't seem to explain it too well.  I've posted on their forum a couple days ago and I've not received a response.  Would someone explain what a callback is and what it's used for?</p>