title: What is a policy in reinforcement learning?
body: <p>I've seen such words as:</p>
  
  <blockquote>
    <p>A policy defines the learning agent's way of behaving at a given time. Roughly
    speaking, a policy is a mapping from perceived states of the environment to actions to be taken when in those states.</p>
  </blockquote>
  
  <p>But still didn't fully understand. What exactly is a policy in reinforcement learning?</p>