title: What does train_on_batch() do in keras model?
body: <p>I saw a sample of code (too big to paste here) where the author used <code>model.train_on_batch(in, out)</code> instead of <code>model.fit(in, out)</code>. The official documentation of Keras says: </p>
  
  <blockquote>
    <p>Single gradient update over one batch of samples.</p>
  </blockquote>
  
  <p>But I don't get it. Is it the same as <code>fit()</code>, but instead of doing many feed-forward and backprop steps, it does it once? Or am I wrong?</p>