Most algorithms are intended to improve the relevance of search results. But some are planned to:
Penalize sites or pages that do not comply with instructions (eg artificial backlinks or keyword stuffing)
Favor sites or pages that have a specific characteristic (eg speed, HTTPS secure protocol, mobile compatibility …)
Google adds, modifies and deletes algorithms permanently (several hundred changes per year). It is important for you to keep abreast of all these evolutions!
Here is the key to remember for search engine algorithm:
Your website must be mobile compatible (according to Google), otherwise your ranking on mobile is worse. This is even more important now that Google switches to a “mobile first” index. You should not display a pop-up or interstitial banner intrusive to the user who arrives from Google.
The main updates of the Google’s algorithm now concern the overall quality of the site. The last one “Fred” would be linked, just like Phantom and Panda.
The last official version of Panda dates from July 2015 but no doubt we will not learn any other date since it is integrated in the general algorithm. It is a major Google’s algorithm.
Penguin was updated on September 23, 2016. It is finally integrated into the Google’s algorithm, with updates “in real time”. This is another major Google’s algorithm.
Google incites to migrate to HTTPS but SEO impact is low
Google has modified its algorithm against satellite pages (attention, their definition seems wide, the impact could concern many people), in place since around the beginning of May 2015