Google Panda is a change to the Google's search results ranking algorithm that was first released in February 2011. The change aimed to lower the rank of "low-quality sites" or "thin sites, and return higher-quality sites near the top of the search results.
Google panda algorithm released in last year. Its a google algorithm for finding the duplicate content in sites. Panda is very affective and penalized all those sites that used copy or duplicate content intheir site. In short we can say that google panda is for checking duplicate content and penalized those site who used this type of contsnt.