Social currency is a term that's now used in the context of social media, but also encompasses the broader idea of basic social interactions, both online and offline. Social currency refers to the value that people have built up in terms of their interactions and their potential for social influence or success.
In some ways, social currency is kind of a vague term. It includes social influence, but it also covers aspects of someone social life that allow them to succeed in personal interactions.
For example, a person's ability to be friendly and make other people ‘feel like insiders’ can be marked as an aspect of personality that builds social currency – even more basic aspects of someone's personality or circumstance can relate to their social currency as well – their smile, their outgoing nature, etc.
Also, we could use social currency to talk about how people achieve goals in social media. If you're looking at the campaign that somebody's done, and various net promoter scores of people who were exposed to a certain social content, you may be able to measure the ‘social currency’ that the person’s social media effort has in that setting.
In general, social currency is like political currency – it denotes the ability to get things done in a social environment. Social currency and political currency are actually very similar in that both are persuasive; one refers more to the political world specifically; another refers to personal interactions in general.