The defining feature of social networks is that nodes represent people. The networks themselves can represent anything from small informal friend groups to entire societies.
Edges in a social network represent a type of relationship between people. Often, this relationship is friendship or communication. However, it can also be something as abstract as the similarity in their video streaming behavior. Just imagine; you might never have met someone, but you could be the only two people in the world who enjoy watching videos of sleeping hippos. That is certainly a kind of relationship!
Many of the tools of network science come from the study of social networks in sociology. The sociologists, Jacob L. Moreno and Helen Hall Jennings, developed the techniques of sociometry, a precursor to modern social network analysis and network science (Moreno And Jennings, 1934...