title: What is a good definition of a "userdata pointer"?
body: <p>I have searched for a good explanation but can't find one. </p>
  
  <p>I could try to write one myself but I'd prefer if someone with better <em>english</em> could help me explain this for Zan Lynx in the comment <a href="https://stackoverflow.com/questions/599365/what-is-your-favorite-c-programming-trick/600523#600523">here</a>.</p>
  
  <p>...and it seems like there should be a good explanation somewhere, why not here?</p>