Help me understand a phrase from the "Java concurrency in practice"
<p>On a page twelve of "Java concurrency in practice" there is a phrase </p>

<blockquote>
  <p>"A good specification defines invariants constraining an object's
  state and post - conditions describing the effect of its operation."</p>
</blockquote>

<p>More or less I undersand the phrase untill the word <code>"post"</code>, then it becomes a garbage.</p>

<p>Can you help please?</p>
