title: What is Train loss, Valid loss, and Train/Val mean in NNs
body: <p>I'm currently learning about Convolutional Neural Networks by studying examples like the MNIST examples. During the training of a neural network, I often see output like:  </p>
  
  <pre><code> Epoch  |  Train loss  |  Valid loss  |  Train / Val
  --------|--------------|--------------|---------------
      50  |    0.004756  |    0.007043  |     0.675330
     100  |    0.004440  |    0.005321  |     0.834432
     250  |    0.003974  |    0.003928  |     1.011598
     500  |    0.002574  |    0.002347  |     1.096366
    1000  |    0.001861  |    0.001613  |     1.153796
    1500  |    0.001558  |    0.001372  |     1.135849
    2000  |    0.001409  |    0.001230  |     1.144821
    2500  |    0.001295  |    0.001146  |     1.130188
    3000  |    0.001195  |    0.001087  |     1.099271
  </code></pre>
  
  <p>Besides the epochs, can someone give me an explanation on what exactly each column represents and what the values mean? I see a lot of tutorials on basic cnn's, but I haven't run into one that explains this in detail.</p>