What does the grave accent symbol (`) ( not single quote) represent in PHP?
<p>In the example below, what do the grave accents in the second line mean?</p>

<pre><code>$cmd = "$ffmpeg -i $video -deinterlace -an -ss $second -t 00:00:01 -r 1 -y -vcodec mjpeg -f mjpeg $image 2&gt;&amp;1";

$return = `$cmd`
</code></pre>
