Reverse SEO is the technique that helps to improve own site's ranking and decrease the competitor's ranking.To do this one has to do huge spamming of the competitor's site with lot of links to other sites.So Google thinks that this site is trying get ranked by huge spamming and so the site gets penalty and disappear from the search engines completely.
Reverse SEO is sort of black Hat SEO technique, in reverse SEO instead of trying to get on the first page of SEO web masters try to remove their competitors from the first page of the SEO.