A spider is a piece of software that follows links throughout the Internet, grabbing content from sites and adding it to search engine databases.

Spiders follow links from one page to another and from one site to another. That is the primary reason why links to your site are so critical. Getting links to your website from other websites will give the search engine spiders more opportunities to find and re-index your site. The more times they find links to your site, the more times they will stop by and visit. This has been true since spiders began. Recently there has been an incredible amount of attention paid to links. That's because Google came clean and said in public that the number and quality of links to your site will directly impact its rankings in the search results.