_(CLOS) is the Common Lisp Object System, an *(object-oriented) *(programming language) embedded in and somewhat integrated into _(Common Lisp).

It is a class-based system, and the first widely-used language to have multiple-dispatch, instance-specific specializers, and method composition. A few artifacts of the fact that it was a late addition to Common Lisp are that it organizes methods into <em>generic functions</em>, a term for Lisp functions which can specialize on their arguments. So it's designed to look like the pseudo-functional style of Lisp while embracing object-orientation.

<ul class="links">
<li>The <a href="http://www-2.cs.cmu.edu/Groups/AI/html/cltl/clm/node260.html#SECTION003200000000000000000">specification</a>.
<li><a href="http://www.cetus-links.org/oo_clos.html">Some links</a>.
</ul>
