title: In Tensorflow, what is the difference between a Variable and a Tensor?
body: <p>The Tensorflow documentation states that a <code>Variable</code> can be used any place a <code>Tensor</code> can be used, and they seem to be fairly interchangeable. For example, if <code>v</code> is a <code>Variable</code>, then <code>x = 1.0 + v</code> becomes a <code>Tensor</code>.</p>
  
  <p>What is the difference between the two, and when would I use one over the other?</p>