title: What does global_step mean in Tensorflow?
body: <p>In this is <a href="https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/tutorials/mnist/mnist.py" rel="noreferrer">tutorial code</a> from TensorFlow website,</p>
  <ol>
  <li><p>could anyone help explain what does <code>global_step</code> mean?</p>
  <p>I found on the Tensorflow website written that <em>global step is used count training steps</em>, but I don't quite get what exactly it means.</p>
  </li>
  <li><p>Also, what does the number 0 mean when setting up <code>global_step</code>?</p>
  </li>
  </ol>
  <pre class="lang-py prettyprint-override"><code>    def training(loss,learning_rate):
          tf.summary.scalar('loss',loss)
          optimizer = tf.train.GradientDescentOptimizer(learning_rate)
          
          # Why 0 as the first parameter of the global_step tf.Variable?
          global_step = tf.Variable(0, name='global_step',trainable=False)
  
          train_op = optimizer.minimize(loss, global_step=global_step)
      
          return train_op
  </code></pre>
  <p>According to Tensorflow doc <em>global_step: increment by one after the variables have been updated</em>. Does that mean after one update <code>global_step</code> becomes 1?</p>