google panda

a change to Google's search results ranking algorithm that was first released in February 2011. The change aimed to lower the rank of "low-quality sites" or "thin sites", and return higher-quality sites near the top of the search results. The name “Panda” comes from Google engineer Navneet Panda, who developed the technology that made it possible for Google to create the algorithm, more effectively policing Internet business practices through use of the google penalty.   

By detecting common black hat SEO techniques, Google penalizes sites that are not operating according to its guidelines. Google penalties forcibly drop the rankings of a site that is deemed to be misbehaving, which can have devastating consequences. Click here for a list of high-profile google penalty cases.