YIKES - what's it all mean?
Well, it has to do with website form security. It is an attempt to keep spammers from using the forms on your website by including a challenge-response component to a form. A common type requires users to type in letters from a digital distorted display, or do math ((((SHUDDER))).
ReCaptcha a system developed at Carnegie Mellon University using digitized text of books to help protect websites from spam bots attempting to use their forms or other restricted area. In 2009, Google acquired it and is currently digitizing documents to use as the recaptcha display.
Handy links
Captcha site: http://www.captcha.net/
WP capcha options: http://wordpress.org/search/capcha