My personal criteria to specifically identify social media apart from other online interaction:

* The platform is a closed garden with a goal to own the content, user submissions, and any personally identifiable data or relationships thereof.

* User interaction is primarily limited by a terms and conditions policy as opposed to a code of conduct. The goal is to impose constraints upon user rights as opposed to user behavior.

* There exists a profit incentive directly tied to engagement frequency. The goal is to quantify content visibility and sell those numbers to third parties.

* Exchange and reselling of user profile data, user submissions, and any analysis or relationship there upon is beyond user control, awareness, or agreement.