title: What is "epoch" in keras.models.Model.fit?
body: <p>What is "epoch" in <code>keras.models.Model.fit</code>? Is it one gradient update? If it is more than one gradient update, then what is defining an epoch?</p>
  
  <p>Suppose I am feeding my own batches to <code>fit</code>. I would regard "epoch" as finishing to process entire training set (is this correct)? Then how to control keras for this way? Can I set <code>batch_size</code> equal to <code>x</code> and <code>y</code> size and <code>epochs</code> to 1?</p>