This was a huge algorithmic change (algorithmic improvement, according to Google) which affected almost 12% of the search results.
The update was rolled out in the US only, with plans to roll it out globally over time.
Google says: “This update is designed to reduce rankings for low-quality sites—sites which are low-value add for users, copy content from other websites or sites that are just not very useful. At the same time, it will provide better rankings for high-quality sites—sites with original content and information such as research, in-depth reports, thoughtful analysis and so on.”
Google farmer is a huge algorithm of google. Google updated its algorithm and now it is called Google Panda.This updation affect almost 20% of search results. This updation is made to decrease the ranking of the sites which have low quality and duplicate content content.It will increase the rank of the sites with unique, original and informative content.