title: What is meant by an "unbound" library or classpath container in Eclipse?
body: <p>While recently imported a new project into eclipse, at one point when I tried to add the GROOVY_SUPPORT library it would up as "unbound" with error-X, like this:</p>
  
  <p><img src="https://i.stack.imgur.com/yEOnB.png" alt="GROOVY_SUPPORT library with red error-X"></p>
  
  <p>It also did not appear in the package explorer as I expected.</p>
  
  <p>What precisely does this mean?  Eclipse did not report any other errors.  All I have it the red-X and the unbound message.</p>
  
  <p>I was able to fix this via futzing with stuff (specifically removing and re-adding the Groovy nature) until it went away, but I'm curious about what was really going on.</p>