How can a compiler compile itself?
<p>I am researching CoffeeScript on the website <a href="http://coffeescript.org/" rel="noreferrer">http://coffeescript.org/</a>, and it has the text</p>

<blockquote>
  <p>The CoffeeScript compiler is itself written in CoffeeScript</p>
</blockquote>

<p>How can a compiler compile itself, or what does this statement mean?</p>