Social Media art is an umbrella that covers a mind-boggling array of projects: performances accompanied by Twitter feeds, paintings inspired by Facebook profiles, online works that evolve as people participate, videos compiled from postings on YouTube, start-up companies created as art. “Social-media art, for me, is defined as anything that uses social media as either a medium, as source material, or as a starting point for critique,” says Hrag Vartanian, editor of Hyperallergic.com, a Brooklyn-based online publication, and the curator of “The Social Graph,” an exhibition that examined the impact of social networking on art, held at Outpost, a nonprofit art space in Bushwick, Brooklyn, last year. “The social graph” is a term coined by Facebook founder and CEO Mark Zuckerberg to describe the way that a network of relationships can be applied to a variety of purposes, such as marketing.