Now that you've asked the question you've got me interested too... according to Wiki Social network:

Quote Originally Posted by Wiki
A social network is a social structure made of nodes (which are generally individuals or organizations) that are tied by one or more specific types of interdependency, such as values, visions, idea, financial exchange, friends, kinship, dislike, conflict, trade, web links, sexual relations, disease transmission (epidemiology), or airline routes. The resulting structures are often very complex.
Interesting, I was just reading about Artificial Neural Networks... I assume the two can be neatly tied together.