Released in February 2011, Google’s Panda Algorithm Update targets websites with poor quality or thin content and reduces their ranking in search results. Panda factors a quality score into Google’s ranking algorithm (PageRank). Websites deemed to have poor quality content receive a low quality score, thus reducing their rankings.
Your quality score isn’t permanent. Panda frequently revisits websites to determine if they’ve improved the quality of their content. So, if you receive a low quality score focus on improving your content so the next time Panda reviews you, you’ll improve.