Also known as delisted or blacklisted. Banned sites are ignored by search engines. This occurs when a URL has been removed from a search engine’s Index, typically for engaging in Black Hat SEO.

It is important to distinguish banned from penalised.  When a site is banned it is completely removed from the search engine index. In contrast, when a site is penalised, it may still rank for certain terms, but will have a lower than expected ranking for it's targetted search terms.

It is easy to check is a site is banned:

1. Seach 'site:www.domain.name' if no results are returned
2. Seach 'link:www.domain.name' if no results are returned
3. Search on the domain name

if there are no results in steps 1 and 2, then it is likely that the site is banned. Low ranking on step 3 is a good indication that the site has been penalised (assuming of course that the site is not a new site and is likely to have been indexed).

The process above refers mainly to Google, but the principles are the same for other search engines.

How to get your site off the Google banned list

If you think that your site has been banned, it can take quite a bit of effort to get your site back onto the Google index. The following are the steps that can be followed to get back on the list:

1. Check that your robots.txt file isn't stopping the Google bot from indexing your site;
2. Make sure that you are not using any black-hat SEO techniques (like cloaking etc.);
3. As far as possible make sure that you conform to the Google Webmaster Guidelines for Quality content;
4. If you have violated the guidelines, admit this at https://www.google.com/webmasters/tools/reconsideration?pli=1 and advise what was done to resolve the issue (be as detailed as possible);