A bad neighbor is any site that have inappropriate online relations. Search engines do penalize sites that use different tricks to manipulate search results. Websites get blacklisted by search engines:

* Sites with spam domains.
* Sites that focus on gambling, adult topics, selling ED Drugs.
* Sites that have a mirror site with exact same web links.
* Sites that try to boost their ranking by using illegal techniques such as keyword stuffing, duplicate content (or lack of any original content), hidden text and links, doorway pages, deceptive titles, machine-generated pages.
* Sites that have uncategorized link directories - Link Farms.
* Sites that have outbound links to sites with bad reputation.