title: What is related_name used for?
body: <p>What is the <code>related_name</code> argument useful for on <code>ManyToManyField</code> and <code>ForeignKey</code> fields? For example, given the following code, what is the effect of <code>related_name='maps'</code>?</p>
  
  <pre><code>class Map(db.Model):
      members = models.ManyToManyField(User, related_name='maps',
                                       verbose_name=_('members'))
  </code></pre>