A social networking service (also social networking site or SNS) is a platform to build social networks or social relations among people who share similar interests, activities, backgrounds or real-life connections. 
A social network service consists of a representation of each user (often a profile), his or her social links, and a variety of additional services such as career services.

Social network sites are web-based services that allow individuals to create a public profile, create a list of users with whom to share connections, and view and cross the connections within the system.

Most social network services are web-based and provide means for users to interact over the Internet, such as e-mail and instant messaging. 

Social networking sites allow users to share ideas, pictures, posts, activities, events, blogs, articles and interests with people in their network.

Online community services are sometimes considered a social network service, though in a broader sense, social network service usually means an individual-centered service whereas online community services are group-centered