Negative SEO (negative search engine optimization)
Negative SEO is the practice of creating a substantial number of trashy backlinks to a website (especially a competitor’s site) with the objective of harming the site by deceptively making the site susceptible and vulnerable to being penalized by Google.
Negative search engine optimization may result in a site’s search rank being unjustly lowered or dropped by Google.
The video below (by former Google software engineer Matt Cutts) addresses some questions regarding negative SEO:
If you suspect that your website has been harmed by negative search engine optimization you may want to consider using Google’s Disavow Tool. By using their Disavow Tool you are asking Google to remove certain URLs from your ranking factor.
Matt Cutts discusses Google’s Disavow Tool in the video below: