Social interaction is any act or practice of two or more people that engages both parties in the awareness of the other. Social interaction does not include two parties who merely have each other in a line of sight.
Social interaction also requires a mutual engagement. One individual spying or stalking another does not count as social interaction because the contact is not wanted by at least one party. This is also true of those people who commit crimes against other people. On the other hand, social interaction does not require both parties to be in the same room as one another, either. Writing a letter to a friend, two parties willingly speaking on the phone or two parties playing an Internet game all count as social interactions.