Google pigeon update or SEO ranking update. Penguin update was an algorithm update made by Google.
Google rolled out penguin update to improve the quality of Google search results. Google started Penguin update in April 2012.
Google penguin update was conducted against the link spamming activities conducted in websites. Mainly manipulative link building activities like paid links (buying and selling links), link exchange, low quality links gained from low quality directories, comment spamming, wiki spamming, unnatural cross linking, unnatural guest blogging etc.
Google conducted more versions of Penguin updates when their first attempt was a great success. Google was able upgrade the quality of their search results.
Penguin 4.0 was conducted in 2016 by which penguin penalties became real time.