title: What does Dense do?
body: <p>What is the meaning of the two <code>Dense</code> in this code?</p>
  <pre><code>self.model.add(Flatten())
  self.model.add(Dense(512))
  self.model.add(Activation('relu'))
  self.model.add(Dropout(0.5))
  self.model.add(Dense(10))
  self.model.add(Activation('softmax'))
  self.model.summary()
  </code></pre>