Reinclusion: After being penalized, websites may file a reinclusion request to the search engine once they've fixed the problem. The search engine will then decide whether or not to put the site back into its search index based on site's brand strength and the infraction's severity.
For example, Google penalized Example.com because the site had been posting spammy, keyword over-loaded, duplicate, low-quality content on its blog. As a result, the site no longer shows up in Google's search engine results pages (SERPs) and consequently receives staggeringly less traffic. Example.com deletes its blog, starts over, and puts fresh, high-quality content on the new one. Example.com may then file a reinclusion request to Google in the hopes the search engine reconsiders.
The first thing a site should do when creating a reinclusion request is to figure out what happened -- why did the search engine penalize you? Was it because you were unknowingly in violation? Did a competitor hijack your site?
Then, explain to the search engine why your site exists and tell them what happened. Tell them the purpose of your site, its overall mission, and how it helps users. Then, explain to the search engine what happened and be completely honest. If you toed their SEO guidelines, tell them. They've heard about every excuse in the book, so it's best to just confess in the long run.
Once you've explained what happened, come clean, and fixed the problems, conclude your reinclusion request by asking if there's anything else you need to do. Tell the search engine you've reviewed their guidelines and can't find anything else that's wrong, but to let you know if something is still wrong.
Lastly, sign it and send the reinclusion request out.