title: Keyword '|' in Makefile Prerequisites
body: <p>The MakeFile below:</p>
  
  <pre><code>afl-fuzz: afl-fuzz.c | test_x86
  gcc afl-fuzz.c -o afl-fuzz
  </code></pre>
  
  <p>What's the meaning of '|' before <code>test_x86</code> ?</p>
  
  <p>The MakeFile is from: <a href="https://github.com/loverszhaokai/AFL/blob/gcc_mode/Makefile" rel="nofollow">https://github.com/loverszhaokai/AFL/blob/gcc_mode/Makefile</a></p>