Social Advertising represents ad formats that engage the social context of the user viewing the ad. Whereas in traditional, non-social, advertising the ad is targeted based on what it knows about the individual person or the individual page, in social advertising the ad is targeted based on what it knows about the individual user's social network.
Social Advertising is the first form of advertising that systematically leverages historically "offline" dynamics, such as peer-pressure, friend recommendations, and other forms of social influence.
Mark Zuckerberg said “Social actions are powerful because they act as trusted referrals and reinforce the fact that people influence people. It’s no longer just about messages that are broadcast out by companies, but increasingly about information that is shared between friends. So we set out to use these social actions to build a new kind of ad system.”
The fact that advertisers are looking to reach out to many social networks at once means that they often look to Ad Networks to deliver ads across these networks through custom applications.
Some other definitions are contextual advertising, or interactive ads.
The key factor that enables Social Ads are independent applications within social networks - now when open known as open social networks or open social platforms. social advertising is also called public service advertising as it is done for benefit of people.