Rather than being a change to the overall ranking algorithm, Panda is more a new ranking factor that has been added into the algorithm (indeed, on our SEO Periodic Table, this would be element Vt, for Violation: Thin Content). Panda is a filter that Google has designed to spot what it believes are low-quality pages. Have too many low-quality pages, and Panda effectively flags your entire site. Being Pandified, Pandification — whatever clever name you want to call it — doesn’t mean that your entire site is out of Google. But it does mean that pages within your site carry a penalty designed to help ensure only the better ones make it into Google’s top results. Get the full story at Search Engine Land