A social signal is a measure of social media activity, such as a vote, share, or other engagement that a search engine might take into consideration as part of its ranking algorithms.
Social signals include:
There is much speculation as to just how much social signals are being integrated into search engine ranking algorithms. Both Google and Bing have confirmed that social signals contribute as ranking signals; however, full disclosure would result in widespread manipulation.
Google has integrated social media data into its Analytics software to help webmasters measure the impact social media has on their websites, which is an indication of how much Google values this data.
It's likely that Google and other search engines have a wealth of data they can use as ranking factors far beyond what they share with the public.
The value of social signals is often confused with the value of the links to web content that they often contain. The value of backlinks have long been a ranking signal for search engines such as Google and Bing; however, links from social media platforms often don't pass equity or PageRank due to the widely implemented nofollow attribute, which is used to discourage link spam.
Because trusted social media accounts, within quality networks, generally interact with quality web content, both Google and Bing use these recommendations to get a clearer picture of the trust, popularity, and authority of web pages they share, link to, and like.
It's unclear as to how much search engines use Facebook data as a ranking signal; however, it's likely used more by Bing than by Google. Bing powers Facebook's Web search functionality, and Bing's Social Sidebar (a third column on its search results pages) allows logged in users to comment on and like Facebook posts relevant to searches without leaving the search engine.
Although Google has no partnership with Facebook, the search engine still has access to the portion of Facebook data available to the open web, and likely uses some of it to gain insights into popularity of web pages.
Google and Bing both struck a deal with Twitter in October 2009 to display real-time updates in their respective search results; however, on July 2 2011, Google's Twitter deal expired. Google lost access to Twitter's real-time feed, or firehose of data, along with any chance of efficiently integrating it into their ranking algorithms. Google terminated its Real-Time Search feature shortly thereafter.
Although Google no longer has access to Twitter's real-time feed, it still has access to public tweets available to the open web, and extracts social signals from some of the data.
Bing still has access to Twitter's real-time data feed, and tweets are included in Bing's own version of "Real-Time Search": its Social Sidebar. Bing's continuing real-time data deal with Twitter—as well as its partnership with Facebook—is key to Bing's successful integration of the social web into web search.
Although Google officially denies using any of Google+'s data as a ranking signal, the usual indirect benefits to search visibility—and more—are present in sharing quality web content on the platform.
It's clear that links and recommendations on the social Web can directly help rankings in regular search results—as well as indirectly—as more shares equal more exposure, and often more backlinks.
As with link building, 90% of the effort should go to creating compelling, useful web content, that people can't help but like and share.