What is Panda or Google Panda that I keep hearing about?

Google Panda is a change to the Google‘s search results ranking algorithm that was first released in February 2011.^[1] The change aimed to lower the rank of “low-quality sites”, and return higher-quality sites near the top of the search results.^[1][2] CNET reported a surge in the rankings of news websites and social networking sites, and a drop in rankings for sites containing large amounts of advertising.^[3]This change reportedly affected the rankings of almost 12 percent of all search results.^[4] Soon after the Panda rollout, many websites,^[5] including Google’s webmaster forum, became filled with complaints of scrapers/copyright infringers getting better rankings than sites with original content. At one point, Google publicly asked for data points^[6] to help detect scrapers better. Google’s Panda has received several updates since the original rollout in February 2011, and the effect went global in April 2011. To help affected publishers, Google published an advisory on its blog, thus giving some direction for self-evaluation of a website’s quality.

http://en.wikipedia.org/wiki/Google_Panda