What is the Raw Post Data
<p>I'm trying to understand the meaning of raw post data. The PHP manual page for <a href="http://php.net/manual/en/reserved.variables.httprawpostdata.php" rel="nofollow"><code>$HTTP_RAW_POST_DATA</code></a> just state that this variable contains <code>Raw POST data</code>. </p>

<p>When this variable will be set and what's the meaning of raw post data?</p>

<p>I understand the <code>$_POST</code> but totally confused with <code>$HTTP_RAW_POST_DATA</code></p>
