As far as I'm aware. Robots are the spiders sent out by search engines like Google, yahoo etc.

By changing the robots meta you can tell them not to index certain pages of your site.

This can also be done using a robots.txt file, which is the more common way of doing it.

For example on my server I've got my site, and also my CMS. My robots file tells the search engine that i don't want it to index my CMS files, this way they won't appear in Google.