A spider is an 8 legged little bug that you don't want crawling on you.:yikes:
:doh1: How could I have been so stupid and forgotten that, even after an entomology class when in college...
Seriously though, it's just the search engines that crawl the site.
They index the pages they crawl for the search engine and assign them some sort of ranking based on words on the page so that when you search for the term "nursing" for instance, they send you to the correct page.
One day...sigh...hopefully, that page at number one will be ultimatenurse.com