Panda was all about eliminating the SEO technique of publishing lots of lower quality, keyword-stuffed articles to influence rankings.
Next came Penguin. The Google Penguin Update launched on April 24. According to Google, Penguin was an “important algorithm change targeted at webspam. The change will decrease rankings for sites that we believe are violating Google’s existing quality guidelines.” Google mentions that typical black hat SEO tactics like keyword stuffing (long considered webspam) would get a site in trouble, but less obvious tactics (link incorporating irrelevant outgoing links into a page of content) would also cause Penguin to flag your site.