title: What does "relu" stand for in tf.nn.relu?
body: <p>In its <a href="https://www.tensorflow.org/versions/master/api_docs/python/tf/nn/relu" rel="noreferrer">API documentation</a>, it says "Computes rectified linear".</p>
  
  <p>Is it Re(ctified) L(inear)... what is U then?</p>