(1) Also known as a "crawler," "robot" (bot) and "intelligent agent," a spider is a program that searches for information on the Web.  Spiders are widely used by Web search engines to index all the pages on a site by following the links from page to page.  The search engine summarizes the content and adds the links to their indexes.  Spiders are also used to locate Web pages that sell a particular product or to find blogs that have opinions about a product.  See 
surface Web and 
bot.
(2) Software that captures a website for browsing offline.  See 
offline browser.
(3) (Spider)  A gaming platform from AMD.  See 
Phenom.