Google Panda is a filter added in Google's search results algorithm to provide better quality contents to Googlers. It was first released in February 2011. The change aimed to lower the rank of "thin content" or "low-quality sites", and return higher-quality sites near the top of the search results. Search Engine Land published a great infographic that explains the history and effects of the Google Panda update right from the beginning.

The Google Panda Update, One Year Later