Proper Defination of Social Sites

Excellent list of attributes

• Identity – a way of uniquely identifying people in the system
• Presence – a way of knowing who is online, available or otherwise nearby
• Relationships – a way of describing how two users in the system are related (e.g. in Flickr, people can be contacts, friends of family)
• Conversations – a way of talking to other people through the system
• Groups – a way of forming communities of interest
• Reputation – a way of knowing the status of other people in the system (who’s a good citizen? who can be trusted?)
• Sharing – a way of sharing things that are meaningful to participants (like photos or videos)

From http://nform.ca/publications/social-software-building-block