BELOW: Example of Facebook Fan Box incorporated into website Sears Drumheller. Discount codes, specials and more are posted for local shoppers to see! A social network service focuses on building and reflecting of social networks or social relations among people, e.g., who share interests and/or activities.

A social network service essentially consists of a representation of each user (often a profile), his/her social links, and a variety of additional services.

Most social network services are web based and provide means for users to interact over the internet, such as e-mail and instant messaging. Although online community services are sometimes considered as a social network service in a broader sense, social network service usually means an individual-centered service whereas online community services are group-centered. Social networking sites allow users to share ideas, activities, events, and interests within their individual networks.

The main types of social networking services are those which contain category places (such as former school-year or classmates), means to connect with friends (usually with self-description pages) and a recommendation system linked to trust.
Popular methods now combine many of these, with Facebook, Bebo and Twitter widely used worldwide; MySpace and LinkedIn being the most widely used in North America.

Source:  Wikipedia.   Read more @ http://en.wikipedia.org/wiki/Social_networking