Auto-redirecting is the technique of automatically sending a site visitor to another page once s/he has landed on a page. The other page is often on the same website, but it can be on a different site altogether. In fact, auto-redirecting is used when a website has been set up for the sole purpose of ranking highly in the search engines. When visitors arrive at a page on the site, from a listing in the search engine results, they are automatically redirected to the main site.
On-site auto-redirecting is common when a page, within the site, has been created specifically to rank highly in the search engines, but has been so highly optimized that it is no good for people to actually see. Auto-redirecting takes visitors to the 'proper' page within the site.
Both of those uses are not wanted by the search engines, and they sometimes penalise a page or site for doing it. Fortunately, the engines are not able to automatically detect most of the auto-redirecting methods.
The engines are not against auto-redirecting when it is done for they what consider to be a valid reason. E.g. when you have posted a message in a forum, you often get a confirmation page which will wait a few seconds and then auto-redirect you to the messages.
