title: What is the difference between async.waterfall and async.series
body: <p>The nodejs async module: <a href="https://github.com/caolan/async" rel="noreferrer">https://github.com/caolan/async</a> provides 2 similar methods, <code>async.waterfall</code> and <code>async.series</code>.</p>
  
  <p>What is the difference between them?</p>