Google Panda Algorithm Update (penalty)
Panda is the name Google gave to the algorithm update it released in February 2011 and was refreshed on a regular basis. The change was intended to weed out “low-quality sites” or “thin content”, and return higher-quality sites in the SERPs (Search Engine Results Pages). As a result, many webmasters thought of it as a penalty, though technically Panda and Penguin are filters, not manually issued penalties. As of March 2013, this algorithm update is built into the live, constantly running Google algorithm and no longer refreshed separately.
Here are some articles related to Google Panda from Ker Communications.