Google is using 3-4 main algorithms that we know of, Penguin, Panda, Hummingbird and Pigeon. There are a few more like payday and pirate but they are for cleaning spammy queries and copyright issues.
Penguin is a Google algorithm which is decreasing search rankings for websites with incorrect SEO. Simply put, Penguin is looking for websites with bad SEO and pushing it down in search results.
Panda is another Google algorithm, which is looking for websites with great SEO and it's pushing it up.
Hummingbird is another Google algorithm update and was the first major update to Google's search algorithm since the 2010 “Caffeine Update”, but even that was limited primarily to improving the indexing of information rather than the sorting of information.
The Pigeon Google algorithm update is aimed to increase the ranking of local listings in a search. The changes will also effect the search results shown in Google Maps along with the Google regular search results.